---
title: "When will my Mac run out of storage? Free calculator"
description: "Enter your free space and daily usage, or two readings, to see how many days until your Mac’s disk is full, the date, and how much to free for 30 days."
url: https://tidymac.space/tools/disk-full-calculator/
updated: 2026-10-16
---

[Home](/) [Tools](/tools/) Mac storage full calculator

# When will my Mac run out of storage?

Divide your free space by how much you use per day: that’s how many days you have left. Enter your numbers below for the exact date and how much to free up to stay 30 days ahead.

Updated October 16, 2026By the Tidy Mac team

Your numbers

Free space now (GB)

GB used per day

![](/img/brand/tidy-128.png)

### Watch your free space from the menu bar

Tidy Mac’s menu bar shows how your free space changed over the last 24 hours, 7 days or 30 days, and notifies you when used space jumps or the disk is almost full. $9.99 once, 2 Macs.

[Download](/download/TidyMac.dmg) [Buy for $9.99 once](/buy/)

## How it works

The calculator assumes a steady rate:

-   **Daily use** = (earlier free space − free space now) ÷ days between the readings, or the number you enter.
-   **Days until full** = free space now ÷ daily use.
-   **To free for a 30-day buffer** = (daily use × 30) − free space now, or nothing if you already have 30 days.

If you’re already short, start with [what to do when your Mac storage is full](/guides/mac-storage-full/), then look at [System Data](/learn/what-is-system-data-on-mac/) and [Time Machine snapshots](/learn/time-machine-local-snapshots/), two common reasons free space disappears.

## Questions

Where do I find my free space?

Choose Apple menu › System Settings › General › Storage, or select your disk in Finder and press Command-I. Both show free space in decimal GB. In Terminal, `df -H /` shows the same decimal units.

How do I know how much I use per day?

Write down your free space today and check again in a week. Enter both readings with the “Earlier reading” option and the calculator works out the daily rate for you.

Why a 30-day buffer?

It gives you a month of normal use before the disk is full, time to notice and clean up calmly. macOS also needs free space for updates and swap; see [not enough space for a macOS update](/guides/not-enough-space-for-macos-update/).

Is the date exact?

No. It assumes you keep using space at the same steady rate. Big downloads, backups or System Data spikes change it. Treat it as an early warning, not a deadline.

## Related

[Mac storage full? What to doGuide](/guides/mac-storage-full/)[What is purgeable space?Guide](/guides/purgeable-space-mac/)[What is System Data?Library](/learn/what-is-system-data-on-mac/)[Time Machine local snapshotsLibrary](/learn/time-machine-local-snapshots/)[GB to GiB converterFree tool](/tools/storage-unit-converter/)[Mac battery health checkerFree tool](/tools/mac-battery-health/)