How to check uptime on Windows, Mac and Linux

"Uptime" means two different things. System uptime is how long a computer or server has been running since it last started: useful when you are troubleshooting, checking whether updates have been applied, or confirming that a server restarted when it should have. Website uptime is the share of time a website responds correctly to visitors, usually given as a percentage such as 99.9%.

This guide covers system uptime on Windows, macOS and Linux. If you need to know whether a website has stayed up, skip to the last section.

Task Manager

Press Ctrl+Shift+Esc to open Task Manager, choose Performance, then CPU. The Up time figure shows days, hours, minutes and seconds since Windows started.

Command Prompt: systeminfo

systeminfo | find "System Boot Time"

This prints the date and time Windows last started. On non-English versions of Windows the label is translated, so run systeminfo on its own and look for the boot time line.

PowerShell

To see how long the system has been up:

(Get-Date) - (Get-CimInstance Win32_OperatingSystem).LastBootUpTime

To see when it last started:

(Get-CimInstance Win32_OperatingSystem).LastBootUpTime

PowerShell 7 also has a ready-made command, Get-Uptime, and Get-Uptime -Since returns the start time.

Why Windows uptime can look too long

If your computer reports days of uptime even though you shut it down every evening, Fast Startup is the likely reason: with it on, Shut down saves the system state to disk rather than fully stopping Windows, so the counter keeps going. Choosing Restart resets it.

Open Terminal (in Applications, then Utilities) and type:

uptime

The output looks like 10:42 up 6 days, 3:15, 2 users, load averages: 1.52 1.61 1.70: the current time, how long the Mac has been up, the number of logged-in users and the load averages.

To see the exact moment the Mac started:

sysctl kern.boottime

Without Terminal, hold the Option key and choose System Information from the Apple menu, then select Software: the "Time since boot" line shows the uptime.

The uptime command works on every mainstream distribution:

uptime

It prints the current time, how long the system has been running, the number of logged-in users and the load averages for the last 1, 5 and 15 minutes.

Two useful options:

uptime -p    # up 6 days, 3 hours, 15 minutes
uptime -s    # 2026-10-09 07:27:41 (when the system started)

For scripts, read the kernel's own counter:

cat /proc/uptime

The first number is the seconds since boot; the second is the time the processors have spent idle, added up across all cores.

To see when the system last booted, and its recent reboot history:

who -b
last reboot

On a remote server, run any of these over SSH, for example ssh user@server uptime.

The three load average numbers that uptime shows on a Mac or Linux are the average number of processes that were running or waiting to run over the last 1, 5 and 15 minutes. Read them against the number of CPU cores: on a four-core server, a load of 4 means the processors are fully busy, and a load well above 4 that keeps rising means work is queuing up. Comparing the three numbers shows the trend: a 1-minute figure far above the 15-minute one means load is climbing.

A very long uptime is not always good news. Many security updates, particularly kernel updates, only take effect after a restart, so a server that has run for a year may be missing important fixes.

A server can have been running for months while the website on it was unreachable, so system uptime says little about what visitors experienced. Website uptime is measured from outside: a monitoring service requests the site every few minutes and records whether it answered correctly, which gives you a history and an uptime percentage.

PulseStack™ website monitoring checks your sites from London, New York and Sydney and alerts you as soon as one stops responding. The Free plan covers 25 monitors with 5-minute checks and needs no card. To check a site right now, use the website down checker, and to see how much downtime an uptime target such as 99.9% allows, try the uptime calculator.

How do I check uptime on Windows?

Open Task Manager (Ctrl+Shift+Esc), choose Performance, then CPU, and read Up time. Or run systeminfo | find "System Boot Time" in Command Prompt, or (Get-Date) - (Get-CimInstance Win32_OperatingSystem).LastBootUpTime in PowerShell.

Why is my Windows uptime so long when I shut down every night?

Fast Startup is the usual reason. With it switched on, Shut down saves the system state to disk instead of fully stopping Windows, so the uptime counter keeps running. A Restart does reset it.

How do I check uptime on Linux?

Run uptime for the time since boot, the number of users and the load averages. uptime -p prints it in plain words, uptime -s shows the date and time the system started, and cat /proc/uptime gives the seconds since boot.

What do the three numbers after load average mean?

They are the average number of processes running or waiting to run over the last 1, 5 and 15 minutes. Compare them with the number of CPU cores: on a four-core machine, a load of 4 means the processors are fully busy.

How do I check the uptime of a remote server?

Run the command over SSH, for example ssh user@server uptime on Linux or macOS. On Windows, use PowerShell remoting: Invoke-Command -ComputerName server { (Get-Date) - (Get-CimInstance Win32_OperatingSystem).LastBootUpTime }.

How do I check a website's uptime rather than a computer's?

Website uptime is the share of time a site responds correctly, measured by checking it regularly from outside. An uptime monitoring service records it for you: PulseStack™ checks your site every few minutes and keeps the history, free for 25 monitors.