What is tax code M1 and why have I got it?

Last reviewed January 2023

A tax code is a string of numbers and letters that tells your employer how your earnings should be taxed. You get one for each Pay As You Earn (PAYE) job you have, and it’s important to keep track of them. Any time your tax code changes, HMRC will alter the Income Tax you’re paying each year.

M1 is a kind of “emergency tax code”, meaning it’s only supposed to be temporary until HMRC has enough information to issue you the right code. The big thing to know about the M1 tax code is that it’s “non-cumulative”, so it doesn’t take into account any tax you’ve already paid in the tax year.

Example of PAYE on tax code M1

Assuming you’re entitled to the standard tax-free Personal Allowance of £12,570, your M1 tax code will be 1257 M1. Because this is a non-cumulative code, the tax you owe in a month will be worked out only from what you made during that month. If you’ve already paid some tax in the year, or used up some of your Personal Allowance, that won’t be factored into how you’re being taxed now.

How to change my M1 tax code

A M1 tax code can be painful if you’re on it incorrectly. Most of the time, HMRC will alter your tax code for you as your circumstances change. However, there are times when you might end up on the wrong tax code – and when that happens you need to get it fixed fast. It’s your responsibility to get the problem sorted, and things can get very tricky if you don’t.

If you think your tax code’s wrong, you need to contact HMRC to make sure they have the information they need to put it right. If you’re claiming a tax rebate with RIFT Tax Refunds, of course, we’ll check your tax code for you as part of the service. If you’re ever given the wrong code, we’ll get it corrected for you.

Could I be due a tax rebate?

Being on the wrong tax code can easily leave you paying the wrong amount of Income Tax on your earnings. For example, this can happen when:

You change jobs and your new employer doesn’t have the information they need to tax your pay properly.
You have a spouse who isn’t using all of their tax-free Personal Allowance, and you’re not claiming Marriage Allowance to transfer a chunk of their allowance to you.
You’ve claimed a tax refund and HMRC has altered your tax code to factor in your expenses. If those expenses change from year to year, your tax code can end up wrong.

Any of these situations can mean you’re paying too much Inc and might be able to claim a tax refund. Get in touch with RIFT to find out more about tax rebates, and to see how the UK’s leading experts can get back everything you’re owed.

Start your claim for free >