Most people who claim marriage allowance notice that their tax code changes — but very few understand what the new code means, how it affects their monthly pay, or what to do if the code looks wrong. This guide explains everything you need to know about marriage allowance tax codes: what each letter and number means, how to calculate the real-world impact on your take-home pay, and how to spot and fix errors.

The Basics: What Is a Tax Code?

Your tax code is a number-and-letter combination that tells your employer (or pension provider) how much income tax to deduct from your pay each month. The most common code in England and Wales is 1257L — the number 1257 represents your personal allowance of £12,570 (multiplied by 10), and the letter L means the standard allowance applies with no unusual adjustments.

When marriage allowance is applied, your code changes — and the changes are different depending on whether you are the partner who transferred the allowance or the partner who received it. If you are still at the stage of deciding whether to apply, our main guide to how marriage allowance works covers the eligibility criteria and application process.

The Two Marriage Allowance Codes

The N Code — For the Transferring Partner (Lower Earner)

If you are the lower earner who transferred part of your personal allowance to your partner, your tax code will change to reflect your reduced personal allowance. Instead of the standard 1257L, you will see a code like 1131N.

• The number 1131 means your effective personal allowance is £11,310 (1131 × 10)
• This is the standard £12,570 minus the £1,260 you transferred
• The letter N indicates that you are the transferring partner in a marriage allowance arrangement

Your N code in plain English: If your tax code is 1131N, it means you have a personal allowance of £11,310. Any income above £11,310 will be taxed at 20% (or Scottish rates if you live in Scotland). The N tells your employer, pension provider, and HMRC that marriage allowance is in effect.

This reduced personal allowance is an important detail that many lower earners overlook. If your income rises above £11,310 — through a pay rise, freelance work, rental income, or savings interest — you will owe tax that you might not be expecting. Our article on the hidden tax trap for lower earners explains exactly how this works and what to do about it.

The M Code — For the Receiving Partner (Higher Earner)

If you are the higher earner who received the transferred allowance, your code will reflect the higher personal allowance. Instead of 1257L, you will typically see 1383M.

• The number 1383 means your effective personal allowance is £13,830 (1383 × 10)
• This is the standard £12,570 plus the £1,260 received from your partner
• The letter M indicates that you are the receiving partner

The practical effect is that each month, your employer deducts less income tax from your pay because a larger portion of your income is treated as tax-free. You do not receive a lump sum — the benefit is spread across the year in smaller monthly deductions.

It is worth noting that the M code is only valid while you are a basic-rate taxpayer. The moment your income exceeds £50,270, you become a higher-rate taxpayer and are no longer eligible to hold the M code. Our guide on marriage allowance and the higher-rate threshold covers exactly where that boundary sits and which income types count toward it.

What This Means Month by Month

For the receiving partner, the M code saves £252 per year in income tax. This is spread across 12 monthly payslips, making the monthly saving approximately £21.

The Full List of Tax Code Letters Relevant to Marriage Allowance

• L — Standard personal allowance. No unusual adjustments. Most common code.
• M — You are receiving the transferred marriage allowance from your partner. Your allowance is higher than standard.
• N — You have transferred part of your marriage allowance to your partner. Your allowance is lower than standard.
• S — You are a Scottish taxpayer. Scottish income tax rates apply.
• C — You are a Welsh taxpayer. Welsh income tax rates apply.
• T — Your tax situation requires individual calculation by HMRC. Sometimes used when both M/N and other adjustments are needed simultaneously.
• 0T — No personal allowance at all. Applied when you have used your entire allowance against another income source.
• BR — All income from this source taxed at basic rate (20%). Often used for second jobs.
• NT — No tax deducted. Rare, typically for non-UK residents.

Scottish Marriage Allowance Codes: SM and SN

If you are a Scottish taxpayer, your marriage allowance codes have an S prefix. The transferring partner receives SN (e.g. S1131N) and the receiving partner receives SM (e.g. S1383M). The calculation of the personal allowance numbers is the same — only the tax rates applied to income above the allowance differ.

The marriage allowance transfer amount (£1,260) and the maximum saving (£252) are the same regardless of where in the UK you live, because marriage allowance is calculated against the UK basic rate of 20%.

Note that in Scotland, the higher-rate threshold is lower than the rest of the UK — currently £43,663. Scottish higher earners receiving the M code need to be more vigilant about income approaching this threshold. See our higher-rate threshold guide for a full breakdown.

How to Check If Your Tax Code Is Correct

Your tax code appears on your payslip, your P60 at year end, and in any tax code notice HMRC sends you. You can also check it online via your HMRC Personal Tax Account at gov.uk. To verify:

Step 1 — Confirm who has which code. The lower earner should have the N code; the higher earner should have the M code. If these are reversed, there is an error.

Step 2 — Check the numbers. The transferring partner’s code should be 1131 (reflecting £11,310). The receiving partner’s code should be 1383 (reflecting £13,830). These figures apply for 2025/26.

Step 3 — Confirm the prefix. Scottish taxpayers should have the S prefix (S1131N / S1383M). Welsh taxpayers have the C prefix.

Step 4 — Do the sanity check. The numbers in the two codes should add up to 2514 (1131 + 1383 = 2514) — double the standard personal allowance of £12,570, confirming the allowance has been correctly split.

Quick check: 1131 + 1383 = 2514 = 2 × 1257 ✓ — if your two codes add up to 2514, marriage allowance has been applied correctly.

What If Your Tax Code Is Wrong?

Wrong Code for the Wrong Partner

If the M and N codes have been assigned the wrong way round — the higher earner has the N and the lower earner has the M — contact HMRC immediately. This means the lower earner is getting a larger personal allowance than they are entitled to, and the higher earner is having too much tax deducted.

Marriage Allowance Code Still Showing After Cancellation

If you cancelled marriage allowance but your code still shows M or N, contact HMRC. For a full guide on what your code should look like after cancellation — and the different scenarios that require cancellation — see our article on when you must cancel marriage allowance.

This situation is also common after separation or divorce, when one or both partners forget to notify HMRC. Our guide on marriage allowance during separation and divorce explains the timeline for when the codes should change and what to do if they don’t.

Similarly, if one partner has died, the codes need updating at the start of the following tax year. Our article on marriage allowance after death of a spouse covers exactly what to do in that situation.

No Code Change After Applying

If you applied for marriage allowance but your code has not changed from the standard 1257L after 4–6 weeks, contact HMRC to check the status of your application. Processing typically takes 2–4 weeks online, but delays do occur.

Mid-Year Code Change

If your code changes mid-year (for example, because you applied in October rather than April), the effect is pro-rated. HMRC will apply the benefit for the remaining months of the tax year, then a full-year code from the following April.

Emergency Tax Codes and Marriage Allowance

If you start a new job and your employer does not have your full tax details, you may be put on an emergency tax code (often W1 or M1 basis). Emergency codes do not reflect marriage allowance — they apply a basic calculation to your pay.

If you are on an emergency code and have marriage allowance in place, you will effectively be ignoring the marriage allowance until your full code is applied. Submit your P45 to your new employer as quickly as possible, or contact HMRC directly to ensure the correct code (including M or N letter) is transferred to the new employment.

Marriage Allowance on Multiple Income Sources

If you have more than one source of income — a main job plus a small pension, or two part-time jobs — the marriage allowance code is applied to your main (highest-income) source. Your secondary income sources typically use a BR code (all taxed at 20% with no personal allowance applied).

This is important because the benefit of marriage allowance only flows through the primary code. If you are self-employed with both employed and self-employed income, the interaction can become more complex — our guide on marriage allowance for self-employed people covers this in detail.

What Your P60 Shows

Your P60, issued at the end of each tax year, shows the tax code applied to your earnings and the total income tax deducted. If marriage allowance was in place for the whole year, you should see the M or N code on your P60. Keep your P60 as evidence that the correct code was applied — it is useful for Self Assessment, mortgage applications, and any disputes with HMRC.

Frequently Asked Questions

My code says 1131M — is that right? No, this would be unusual. The M code should come with the higher number (1383M for the receiving partner). The lower number (1131) should be accompanied by the N code. Contact HMRC to check whether this is an error.

My code is 1257L even though I applied for marriage allowance two months ago. What should I do? Wait one more week, then call HMRC on 0300 200 3300. If it has been more than 4 weeks since a successful online application, HMRC should be able to investigate and confirm whether your application was received and processed.

I left my job mid-year and my new employer has given me an emergency code. Will I lose my marriage allowance? Not permanently. Submit your P45 to your new employer immediately, or contact HMRC to ensure the correct code (including N or M) is transferred. Any overpaid tax from the emergency code period will be recovered through a year-end reconciliation.

How do I see my tax code online? Log in to your HMRC Personal Tax Account at gov.uk. Your current tax code is displayed on the main screen, along with a breakdown of how it has been calculated — including the personal allowance and the marriage allowance component.

What if I have the N code but I earn more than £11,310 this year? You will owe tax on income above £11,310. Your employer will deduct this automatically through PAYE if your code is correct. If you are self-employed, declare all income on your Self Assessment return and HMRC will calculate the tax owed. See our lower earner tax trap guide for a detailed breakdown of how much extra tax you could owe at different income levels.

Final Thoughts

Tax codes are HMRC’s primary tool for collecting the right amount of tax through PAYE, and marriage allowance works by adjusting those codes. Understanding what your M or N code means — and being able to verify that it is correct — takes about five minutes and could save you from either overpaying or unknowingly underpaying tax.

The most important habit is to check your tax code at the start of each new tax year (April) and whenever you change jobs. If the code does not match what you now know to expect, contact HMRC to correct it.

For everything else connected to how marriage allowance works in practice, our full cluster of guides covers the lower earner tax trap, self-employed eligibility, investment income and adjusted net income, the higher-rate threshold, when to cancel, separation and divorce, and death of a spouse.