How to Clear CMOS: Three Methods That Work

A CR2032 CMOS battery being lifted out of a motherboard with a screwdriver

Short answer: Shut the PC down, unplug it from the wall, then hold the power button for about 30 seconds to drain residual power. Then use one of three methods: press and hold the Clear CMOS button for 30 seconds, bridge the CMOS jumper pins with a screwdriver for 30 seconds, or remove the CR2032 battery from the motherboard. Removing the battery is the most reliable.

Clearing the CMOS resets your motherboard's stored settings back to defaults. It is one of the first things worth trying when a PC will not start after a BIOS change, a hardware swap, or a failed overclock. It is also completely reversible and costs nothing, which is why it sits so early in most troubleshooting flows.

What CMOS actually is

CMOS stands for Complementary Metal-Oxide-Semiconductor. In this context it refers to a small, battery-powered memory chip on your motherboard, usually paired with a real-time clock, that stores the foundational settings your system needs in order to start.

The important characteristic is that it is volatile memory. Cut its power for long enough and it erases itself back to a clean slate. That is the entire mechanism behind every method below: you are not pressing a magic reset, you are depriving a chip of power.

Before you start: drain the power

Do this first, whichever method you use. Skipping it is the most common reason a CMOS clear does not take.

Shut the PC down fully.
Unplug the AC power cable connecting the power supply to the wall or surge protector.
Press and hold the power button for about 30 seconds. Nothing will happen visibly. You are discharging residual power held in the system.

Method 1: the Clear CMOS button

Some motherboards include a dedicated button for this, labelled something like CLR_CMOS. It is usually on the rear I/O panel or on the board itself.

With the power drained, press and hold that button for about 30 seconds. Release it, reconnect the PC to power and start the system.

Motherboard rear panel Clear CMOS button labelled CLR_CMOS — Some boards have a dedicated button, often on the rear I/O.

This is the easiest method and it is also the least reliable of the three. If the system behaves the same afterwards, try one of the methods below before concluding that CMOS was not the problem.

Method 2: the CMOS jumper pins

This is the oldest and most widely available method. Nearly every motherboard has a pair of jumper pins for it, though the label varies:

RESET_BIOS
CLR_CMOS
CLEAR_CMOS
CLR_BIOS
JBAT1

Find the exact location in your motherboard manual, because the position moves between boards and guessing is a bad idea.

CMOS clear jumper pins on a motherboard — Jumper pin labels vary: CLR_CMOS, JBAT1, RESET_BIOS and others.

With the power drained, bridge the two pins with a conductive object. Some boards ship a plastic jumper cap on a 3-pin header for this purpose. If yours does not, the tip of a metal screwdriver or a house key works fine.

Hold the bridge across both pins for about 30 seconds, then release, reconnect power and start the system.

Screwdriver tip bridging two CMOS jumper pins on a motherboard — A screwdriver tip or a house key works as the bridge.

Method 3: remove the CMOS battery

This is the most effective method, because you are removing the power source entirely rather than shorting a circuit.

The battery is almost always a CR2032 button cell sitting somewhere on the motherboard. Your motherboard manual will give the exact location.

CR2032 CMOS battery seated on a motherboard — The CR2032 cell, held by a small spring latch.

With the system powered off and unplugged, locate the battery.
Most are held by a small spring latch. Compress the latch from inside the socket, towards the squared cut-out.
The battery will lift on one side or pop out entirely. If it is stubborn, the tip of a screwdriver or a pen gives you better access to the spring.
Leave it out for a minute, then refit it the same way up.

If you have an ITX motherboard, the battery may be a different type connected by a wire rather than a socketed cell. Check your manual before pulling on anything.

What to do after clearing the CMOS

When you start the PC you will most likely see a message telling you the system settings have changed. That is expected. It is the motherboard telling you it has come up on defaults.

Go into the UEFI/BIOS and check your settings before you carry on using the machine:

Loading Optimized Default Settings is enough for most people.
Depending on your system, you may need to reconfigure specific settings such as Secure Boot, which some games and anti-cheat systems require.
If you had XMP or EXPO enabled for your memory, it will now be off. Our guide to enabling XMP and EXPO covers turning it back on.
Your system clock will likely need setting.

Do I need to replace the CMOS battery?

Usually not. The CMOS chip draws a tiny amount of power to hold its settings, so a single battery commonly lasts well over five years without any trouble.

The symptom that points at a dead battery is your PC failing to retain CMOS settings between restarts. If your clock resets, or your BIOS settings revert every time you power down, the battery is likely worn out and a fresh CR2032 will fix it.

Frequently asked questions

Will clearing the CMOS delete my files?

No. CMOS holds motherboard settings only. Your drives, your operating system and your files are untouched.

How long do I need to leave the CMOS battery out?

A minute is plenty once you have drained residual power by holding the power button with the PC unplugged. Draining first matters more than how long the battery stays out.

Do I have to unplug the PC to clear the CMOS?

Yes. Every method assumes no power is reaching the board. Clearing CMOS on a system still connected to mains power will often do nothing at all.

Will this fix a PC that will not POST?

Sometimes, particularly if the problem started after a BIOS change, a memory overclock or a hardware swap. It is not a cure-all. Reseating RAM and the graphics card should come first, which our guide to a PC that will not turn on walks through.