How to track what's growing on your Mac's disk over time

To track disk usage over time on a Mac, you need a record, because macOS doesn't keep one. Storage settings, Finder and Disk Utility each show today's figures and nothing about last week. Note your free space and the largest Storage settings categories once a month, compare them, and the category that keeps growing tells you where to look.

From there, Finder narrows it down. Folder sizes in list view show which folder grew, and a Smart Folder can list every large file changed in the last month. Disk Utility shows Time Machine's snapshots with their sizes. Activity Monitor's Disk tab shows what's writing right now, which isn't the same as what's using space.

If you'd rather not keep notes, a few apps keep a history for you, including the one this site is for. The post on why Mac storage keeps filling up covers the causes in depth. This one is about watching: what to measure, how often, and how to read what you see.

Why a Mac's disk fills a little at a time

Most space isn't lost in one go. It goes a few hundred megabytes at a time, to things that are added often and removed rarely, so no single day looks unusual. Tracking works because the trend shows what a single day hides.

What usually grows?

Here are the usual growers, based on what each owner does with them. All of them grow while you use your Mac normally, and only some give space back by themselves.

What grows	Why it grows	Where Storage settings counts it	Gives space back by itself?
App caches	Apps keep data to load things faster	System Data	Partly, when space runs low
Messages attachments	Every photo, video and file in your chats	Messages	Only if Keep messages isn't Forever
Photos library	New photos and videos, and their previews	Photos	Only with Optimize Mac Storage
iPhone and iPad backups	Each backup made on this Mac	iOS Files	No
Time Machine local snapshots	Files changed while a snapshot exists	System Data	Yes, after 24 hours or when space is needed
Document versions	Earlier versions apps save as you edit	System Data	Managed by macOS
Games and developer tools	Installs, updates, builds and downloads	Applications, Developer or System Data	Rarely

Three shapes of growth

When you plot or list your numbers, growth tends to take one of three shapes, and each points somewhere different:

• A steady climb. A little more each week, never less. Messages, the Photos library and app caches grow like this.
• A step. Nothing for weeks, then several gigabytes at once. A new iPhone backup, a game, a macOS upgrade or a large download looks like this.
• A sawtooth. Up and down within days. Time Machine's snapshots, swap files and caches that macOS clears when space runs low move like this.

Steps are the easiest to explain, because you can usually match them to something you did that day. Climbs are the ones tracking catches, because they hide in day-to-day noise.

How long before a trend means something?

Two or three readings in the same direction. One month's rise can be a step you've forgotten about, or a sawtooth caught at its peak. A category that rises at each of three monthly readings is growing, whatever any single day says, and that's when it's worth finding the folder behind it.

How much daily change is normal?

There's no published figure, and it depends on how you use your Mac. A few hundred megabytes that come and go are a Mac working normally: caches fill, logs gain lines, and a snapshot taken every hour holds on to what changed in that hour.

What's worth noticing is direction. If free space only falls for several weeks, or drops by tens of gigabytes overnight, something is growing faster than macOS gives space back, and a record lets you find out what.

What macOS shows you, and what it doesn't

macOS has good tools for looking at storage today. None of them remembers yesterday. Knowing what each shows helps you pick the right one for each question.

Storage settings: today's figures only

Choose Apple menu › System Settings, click General in the sidebar, then Storage. The bar shows used and available space by category, and All Volumes shows each volume on the internal disk in more detail. Categories with an information button list their largest items.

It shows nothing about change. A category doesn't say whether it grew, and there's no date beside the totals. Before macOS Ventura, the same figures were under Apple menu › About This Mac › Storage, with the same limit.

Finder: sizes and dates, folder by folder

Finder can show a folder's size, and when it last changed. In list view, choose View › Show View Options and select Calculate all sizes, and folder sizes appear in the Size column.

File › Get Info, or Command-I, shows one item's size. View › Show Status Bar shows the available space at the bottom of every Finder window, which is the quickest number to note.

The Date Modified column is useful for tracking: a folder's date usually changes when an item directly inside it is added, removed or renamed, though not always for changes deeper down. Sorting by it shows which folders were active recently. The post on seeing folder sizes in Finder covers the settings in detail.

Disk Utility: available space and snapshots

Select your startup volume in Disk Utility's sidebar and click Info in the toolbar for its capacity, used and available space. Apple notes that available space can include purgeable space, which macOS frees when it's needed, so Disk Utility's figure can be larger than Finder's.

Choose View › Show APFS Snapshots to list the volume's snapshots at the bottom of the window. Columns you can show include Date Created, Private Size and Cumulative Size, and the action menu can copy the table's rows, so you can paste them into a note.

Activity Monitor's Disk tab: writes, not space

Open Activity Monitor from the Utilities folder in Applications and click Disk. Apple says it tracks how often your Mac reads and writes, and the amount of data read or written. Click the Bytes Written column heading to put the busiest processes at the top.

That's activity, not storage. A process that rewrites the same file all day can write a lot and use almost no space, and a file copied once can use a lot after writing it once. Use the Disk tab when free space is dropping while you watch, to see who's writing.

Is there a storage history anywhere in macOS?

No. Time Machine keeps a history of your files, not of how much space they take, and its local snapshots last 24 hours. The warning that your startup disk is almost full arrives when the disk is already tight, not when the trend starts.

Tool	What it shows	Keeps a history?	Best for
Storage settings	Space by category, largest items	No	The monthly snapshot
Finder list view	Folder sizes, dates changed	No	Finding the folder that grew
Finder Smart Folder	Files matching rules you set	Updates live, no history	Large files changed recently
Disk Utility	Available space, snapshots and their sizes	No	Checking snapshots
Activity Monitor	Data read and written per process	No	What's writing right now

How to track disk usage over time on a Mac by hand

A record doesn't need to be elaborate. Five numbers a month, written in the same place, are enough to see a trend after two or three months.

What should you write down?

Each time, note:

1. The date.
2. Available space, from Storage settings or Finder's status bar.
3. The four or five largest categories in Storage settings, with their sizes.
4. Anything unusual you did since last time, such as a new iPhone, a macOS upgrade or a big project.
5. If you track folders too, the sizes of the same five or six folders each time.

The last item is what turns numbers into answers. A 15 GB jump with "set up new iPhone" next to it needs no investigation.

A note, a spreadsheet or screenshots?

Any of them works. A single note in Notes with one dated line per visit is the quickest. A spreadsheet in Numbers can draw a line chart of free space or of each category, which makes a slow climb obvious.

To chart it, put the dates in the first column and one category per column beside them, select the table, click Chart in the toolbar and choose a line chart. Each category becomes a line, and the one that only goes up stands out.

Screenshots are the least effort. Press Shift-Command-5 to open Screenshot, capture the Storage settings window, and keep the images in one folder. You lose the ability to chart them, but you keep every category, not just the ones you thought to write down.

When should you measure?

At about the same time of day, and not straight after a big change. Copying a large project to the Mac and then moving it off leaves it held by Time Machine's snapshots for about a day, which inflates System Data until they expire.

A restart clears swap files, so measuring soon after one gives a steadier System Data figure. Wait for Storage settings to finish counting before you note anything; its totals can take a minute to settle.

Which folders should you measure in Finder?

Start with the folders in your home folder: Downloads, Documents, Movies, Music and Pictures. Then the large folders in your Library folder: Application Support, Caches, Containers and, if you write code, Developer. Hold down Option and choose Go › Library in Finder to open it.

You don't need all of them every month. Measure the ones Storage settings points to. If System Data grew, start in the Library folder; if Documents grew, start in Downloads and Movies.

Here's what a few months of notes can look like, on a hypothetical Mac.

Date	Available	System Data	Documents	Messages	Photos	Note
1 July	64 GB	31 GB	58 GB	19 GB	42 GB
1 August	49 GB	33 GB	61 GB	24 GB	47 GB	Holiday photos
1 September	42 GB	32 GB	63 GB	29 GB	48 GB
1 October	34 GB	34 GB	64 GB	34 GB	48 GB

In this example log, Photos stepped up in August and then settled, which matches the holiday. Messages climbed 5 GB every month with no event to explain it. That's the one to look at.

How long should you keep the log?

At least a year. A year of lines shows the patterns that repeat: a new phone and its backup, a macOS upgrade each autumn, holidays full of photos and video. Once you know your Mac's usual year, an unusual month stands out at a glance.

What about an external drive or a second Mac?

Storage settings covers the internal disk, so track an external drive in Finder: select it in the sidebar and choose File › Get Info, or check Disk Utility. Give each drive and each Mac its own line in the log. A backup drive that fills steadily is normal; Time Machine deletes the oldest backups when it's full.

A Smart Folder that shows recent large files

Folder sizes show where space went; a Smart Folder shows which files arrived. It's a saved Finder search that updates by itself as files change, so you can leave it in the sidebar and glance at it each month.

How do you make one?

1. In Finder, choose File › New Smart Folder.
2. Click This Mac so it searches the whole Mac.
3. Click the Add button on the right, below the search field. In the first pop-up menu choose Other, select File Size, and click OK.
4. Set it to is greater than and enter a size, such as 500 MB.
5. Click the Add button again, choose Last modified date, then within last and 30 days.
6. Click Save, give it a name such as "Large and recent", and keep Add To Sidebar selected.

Click it in the sidebar whenever you like. Apple notes that the list updates automatically as files that meet the criteria are added, changed or deleted. To change the rules later, open it and choose Show Search Criteria from the action menu.

What does it find, and what does it miss?

It finds single large files: a screen recording, an exported video, a disk image, a backup archive, a virtual machine's disk. Those are often the step changes in your log, and the Smart Folder names them in seconds.

It misses growth spread over thousands of small files, such as an app's cache, a Messages attachments folder or a developer tool's downloads. No single file there is large. It also relies on Spotlight, so anything Spotlight doesn't index won't appear. For those, compare folder sizes instead.

Which variations are worth saving?

• New arrivals. Created date within the last 7 days, and file size greater than 100 MB. It shows what came onto the Mac this week.
• Large and forgotten. Last opened date before a date a year ago, and file size greater than 1 GB. These are candidates for an external drive.
• Videos only. Kind is Movie, and file size greater than 1 GB. Video is often the largest thing people make themselves.

Deciding which big files you no longer need is a separate job. Here the point is watching what changes, so keep the rules about dates, not just sizes.

Can a Smart Folder search system files?

By default, Finder searches leave out system files. In the first pop-up menu, choose Other and add System files, set to are included, to widen the search. Even then it lists only what Spotlight has indexed, so it's a complement to folder sizes rather than a replacement.

Reading the trend: what each kind of growth points to

A log is only useful if it leads somewhere. Once one category or folder stands out, match its shape to its likely cause, then go to the setting that controls it rather than deleting the same files again next month.

A steady climb in Messages or Photos

Messages keeps every attachment until you delete it in Messages, or set Keep messages to a shorter time in Messages › Settings › General. If Messages climbs every month, check that setting first. The post on Messages taking up space shows how to trim old attachments safely.

Photos grows with every photo your devices take. With iCloud Photos, Optimize Mac Storage keeps smaller versions on the Mac. Change the Photos library only in Photos; changing files inside it in Finder can damage it.

A steady climb in System Data

App caches are the usual climber. Apps recreate them when they need them, and folders from apps you've deleted stay behind. That's normal, and macOS clears safe ones when space runs low; clearing them by hand frees space, but it doesn't make your Mac faster.

If the climb is steeper, check Activity Monitor's Disk tab for what writes in the background. A process called bird is one of the system processes behind iCloud Drive; the post on bird and iCloud's local cache explains when its data is worth a look. Developer tools are the other common climbers.

A step up you can match to an event

A new iPhone backup, a game or a macOS upgrade shows up as a step on the day it happened. Each new backup updates its device's folder, and backups of devices you no longer have stay until you delete them.

Games are often tens of gigabytes each. Steam keeps them in its own folder, and uninstalling a game in Steam is the way to get the space back; the post on Steam games and Mac storage covers where they live.

A steady climb in Documents

Documents counts files in your home folder that no other category claims, so recordings and exports often land here. Zoom, for example, saves local meeting recordings in a folder for each meeting inside ~/Documents/Zoom, and a long meeting can take several gigabytes. Screen recordings and exported videos go wherever you saved them.

The Smart Folder above usually names these within seconds. They're your files, so the choice is to keep, archive to an external drive, or delete.

Space that comes and goes

Up one day, down the next is usually Time Machine's local snapshots or swap. Apple says snapshots are kept for 24 hours, your Mac counts their space as available, and Time Machine deletes them as they age or as space is needed. A restart clears swap. Neither needs action.

Free space falls but no category grew

Look at the categories that don't have an information button. Other Users & Shared counts files created, modified or shared by other accounts on the Mac, so someone else's photos or downloads can take your free space. Each account needs its own look, signed in as that person.

The macOS category holds system apps and files, so it can change after an update. Like System Data, it shows a size only: Apple's guide says you can't select or delete files in it, because macOS manages them.

Growth you can't place

If System Data rises and nothing in your Library explains it, check two places macOS manages itself. Disk Utility's snapshot list may show an old snapshot from another backup app. And a hidden folder at the top of the disk keeps earlier versions of documents; the post on document versions on a Mac explains when it grows.

Shape	Likely cause	What to do
Steady climb in Messages	Keep messages set to Forever	Change Keep messages, trim in Messages
Steady climb in Photos	New photos, full-size originals	Optimize Mac Storage, or an external library
Steady climb in System Data	Caches, background sync, developer tools	Find the folder; use the owner's settings
Step up in iOS Files	A new backup	Delete backups of old devices
Step up in Applications	A game or large app	Uninstall what you don't use
Up and down	Snapshots, swap	Nothing; they give space back

A worked example: three months of notes

Here's how tracking plays out on a hypothetical Mac: a 512 GB MacBook Pro used for work and some app development, with free space falling from 140 GB to 95 GB over a summer.

The first month

Storage settings shows System Data up by 18 GB and everything else steady. The owner restarts and checks again the next morning: System Data is still up by 16 GB. Disk Utility's snapshot list shows only the last day's hourly snapshots, so snapshots aren't the cause.

In Finder, the Library folder's Developer folder is 14 GB larger than the note from the start of the month. That's where the growth is.

The second month

The note now tracks the Developer folder's main subfolders. Xcode's DerivedData holds build files for six projects, two of them finished long ago, and the simulator devices folder has grown with each new iOS release. Those are build files and test devices, not work.

Xcode's own settings remove old simulator runtimes, and DerivedData folders for finished projects go to the Trash with Xcode closed. The post on removing developer tools you don't use covers the rest of what had piled up.

The third month

With the developer folders under control, the log shows a different climb: Messages up by 4 GB a month. Keep messages is set to Forever, and a family group chat shares a lot of video. The owner changes it to one year.

By the end of the third month, free space is back to 150 GB, and the log has become a five-minute habit.

What it didn't need

No app was cleared on a schedule, no cache was wiped, and nothing was deleted on a hunch. Each fix came from a number that moved two months running.

Each fix was also made in the owner's own settings: Xcode's, then Messages'. Tracking made the decisions small and specific. The post on a monthly Mac maintenance routine builds the same check into ten minutes a month.

Other tools that keep a history

If you'd rather not keep notes, some apps record measurements for you. They differ in what they measure and how often, so check what each one actually keeps.

StorageRadar

StorageRadar is a disk analyzer for macOS whose site says it can capture snapshots of a scan and compare what grew, shrank, appeared or disappeared. Its site says snapshots stay on your Mac, that the free tier and Core can capture snapshots and review their history, and that the Developer tier unlocks comparing and exporting them.

Because it works from scans, its history has a point for each scan you take, so the trend depends on scanning regularly.

iStat Menus

iStat Menus, from Bjango, shows used and free space and disk activity in the menu bar, alongside CPU, memory and network readings. Its site says it can notify you when disk space is low. It suits people who want a constant readout rather than a folder-by-folder history.

Does Time Machine show how much changed?

Not directly. Apple says Time Machine backs up only the files that changed since the previous backup. So a routine backup that suddenly takes far longer than usual often means a lot changed since the last one, and the Smart Folder above is a quick way to see what.

Disk maps and analyzers

Most disk analyzers show one scan at a time: a map of where space is today. You can still track with them by scanning on the first of the month and saving a screenshot of the map. The comparison of disk space analyzers for Mac covers what each one shows.

What should a tracking tool do?

• Keep history on your Mac. File names and paths say a lot about you; a history of them shouldn't need an account or a server.
• Measure without a full scan every time. Watching known folders lightly takes far less work than rescanning the whole disk every day.
• Say what grew, not just how much. A total that fell by 20 GB is a prompt; a folder name is an answer.
• Alert without alarm. A warning should say what changed and leave the decision to you.

Mistakes to avoid when tracking disk usage

Tracking is simple, but a few habits make the numbers misleading or lead to the wrong fix.

Tracking only the total

Free space alone tells you that something grew, never what. Two categories can move in opposite directions and cancel out, hiding a steady climb. Note the largest categories as well, even if it's only three of them.

Comparing numbers from different tools

Storage settings, Finder and Disk Utility can disagree about available space, mainly because of purgeable space and snapshots. Pick one source for each number in your log and stick to it. A change between two tools isn't a change on your disk.

Measuring right after a big copy

Files you copied to the Mac and removed the same day can stay held by snapshots for up to 24 hours. Measure the next day, or note the copy beside the number so you know why System Data jumped.

Reacting to one day's number

A single high reading is usually a sawtooth at its peak. Look for the same direction across two or three readings before you go hunting. The exception is a sudden drop of tens of gigabytes, which is worth checking straight away.

Deleting what grew without knowing what it is

Some folders that grow must not be cleared in Finder: the Photos library's insides, iCloud Drive and other cloud folders, and Messages' attachments folder, which leaves conversations with missing attachments. Use each app's own controls. Move anything else to the Trash first, so it can be put back.

Clearing caches every time the number rises

Caches climb back as you use your apps, so clearing them on a schedule buys the same space again and again, and apps are slower while they rebuild. Leave caches unless one has grown far beyond the others or belongs to an app you removed.

How the app does it

Wombit keeps the history macOS doesn't. A small part of the app can stay in the menu bar, showing available space and keeping a daily history from the day you install it. It only reads, and nothing about your files leaves your Mac.

It measures free space every hour. Once a day, at low priority, it measures the places the catalog knows by a fixed path, such as caches, simulators, Docker, package caches, AI models and backups. Each full scan of the startup disk also records every folder of 500 MB or more, so you can see what grew since the last scan.

What Changed shows the Last 7 Days, the Last 30 Days or Since Last Scan. It starts with the answer, such as how much used space grew, then shows each day and which places grew or shrank. Alerts can tell you when space is low, or when something grows by 10 GB or more in a day.

Select anything that grew to see what it is and how safe it is to remove. App caches are Safe. Messages attachments and iPhone backups are Review first, so nothing starts checked. Snapshots and the Photos library are Managed by macOS: explained, and handled through macOS's own mechanism.

• ~/Library/Caches/*

  App caches

  Data that apps and macOS services keep so they can load things faster. Apps create it again when they need it.

  Safe · Moves it to the Trash

• ~/Library/Messages/Attachments

  Messages attachments

  Photos, videos, audio messages and files sent and received in Messages on this Mac.

  Review first · Explained only: the app shows you how

• ~/Library/Application Support/MobileSync/Backup/*

  iPhone and iPad backups

  Backups of an iPhone, iPad or iPod touch that were made on this Mac, one folder for each device.

  Review first · Moves it to the Trash

• ~/**/*.photoslibrary

  Photos library

  A Photos library: your photos and videos, your edits and albums, and the previews Photos makes from them.

  Managed by macOS · Explained only: the app shows you how

• Time Machine local snapshots

  Hourly snapshots of your startup disk that Time Machine keeps on the disk itself, so you can restore files even without your backup disk.

  Managed by macOS · Runs tmutil for Time Machine's own snapshots, through the helper

The menu bar item and its meter are free, and history is kept for everyone from the first day. What Changed and its alerts are PRO, one payment of $4.99 with lifetime access, so upgrading shows the history you already have.