Tax code calculators
Compare two tax codes
Old code against new, BR against 1257L, 0T against your normal code: the same pay through both, payslip by payslip and over the year.
BR takes more over the year
£2,516.00
| 1257L | BR | |
|---|---|---|
| Tax-free amount | £12,570 | none |
| Tax, first month | £390.20 | £600.00 |
| Tax over the year | £4,684.00 | £7,200.00 |
| Take-home after tax | £31,316 | £28,800 |
Same pay every month, HMRC’s cumulative method, Income Tax only (no National Insurance).
Two codes on the same pay can take very different amounts of tax, and the difference is rarely obvious from the codes themselves. On £36,000 a year paid monthly, 1257L takes £4,684.00 over the year by HMRC's cumulative method. The same pay on BR, with no allowance and everything at 20%, takes £7,200.00, which is £2,516.00 more. On 0T, also without allowance but with the normal bands, it takes £7,200.00. A smaller change, from 1257L to 1100L after a company benefit of £1,570, costs £314.00 over the year. The comparator above runs both codes through the same payroll calculation for your pay and frequency, so you can see what a new code from HMRC changes before it reaches your payslip, or how far a wrong code is from the right one.
What a new code number changes
Change in tax each month
+£21.00
| Allowance change | −£1,260 |
| Tax over the year with 1257L | £3,484.00 |
| Tax over the year with 1131L | £3,736.00 |
Rules read on HMRC’s texts by Radif Partners · Editorial policy · Method
Eight codes on £36,000 a year
The table runs one salary through codes people commonly find on their payslips in 2026 to 2027. The figures are Income Tax only, with equal monthly pay, from HMRC's payroll method (PAYE specification).
| Code | Tax in month 1 | Tax over the year | Pay after tax |
|---|---|---|---|
| 1257L | £390.20 | £4,684.00 | £31,316 |
| 1383M | £369.20 | £4,432.00 | £31,568 |
| 1131N | £411.20 | £4,936.00 | £31,064 |
| 1100L | £416.40 | £4,998.00 | £31,002 |
| BR | £600.00 | £7,200.00 | £28,800 |
| 0T | £600.00 | £7,200.00 | £28,800 |
| K475 | £730.06 | £8,763.60 | £27,236.40 |
| S1257L | £392.27 | £4,708.97 | £31,291.03 |
Three groups stand out. Codes with an allowance (1257L, 1383M, 1131N, 1100L) differ by 20% of the change in allowance while the pay stays in the basic rate band. Codes without one (BR, 0T) remove the whole allowance. K codes go further and add to taxable pay, and an S prefix switches to the six Scottish bands.
Reading a change of code
When HMRC sends a new code, the change in its number times ten is the change in your tax-free pay, and the tax effect is that amount times your top rate. From 1257L to 1131N is £1,260 less allowance, about £252 more tax over the year for a basic rate taxpayer; the partner receiving it on 1383M pays the same amount less. A change of letter alone, L to T for example, does not change the tax: the number does.
Two codes on the same pay
BR against 0T, over the year
−£4,460.00
| Tax with 0T | £16,460.00 |
| Tax with BR | £12,000.00 |
| Each month | £371.67 |
Cumulative codes against the week 1 basis
The comparator also shows what an emergency basis does. Put 1257L in one box and 1257L M1 in the other with the same yearly pay: the totals are almost the same, because equal monthly pay gets one month's allowance either way. The gap appears when pay is uneven or when the job starts after April, because the cumulative code gives back the allowance of the months already gone while the month 1 basis never does. The emergency tax calculator handles that case with a start month.
The same logic explains a refund on a payslip after a code goes up. Say HMRC moves you from 1100L to 1257L in month 7: the cumulative calculation recomputes the tax due to date with the higher allowance for all seven months, sees that too much was paid in months 1 to 6, and gives the difference back on that payslip. The yearly figures in the comparator are what each code would take if it applied all year, so the refund is roughly the yearly gap times the share of the year already paid.
Scottish and Welsh prefixes
Comparing 1257L with S1257L on the same pay shows what moving to or from Scotland means for your Income Tax: the allowance is the same, but the six Scottish bands start at 19% and reach 42% from a lower point than the higher rate in England. C1257L gives the same result as 1257L in 2026 to 2027, because the Welsh rates add up to the English ones in every band.
When to compare
Use it when a coding notice arrives, when your payslip shows a code you did not expect, or when you have two jobs and want to see what happens if the allowance sits on one or the other. For the full picture of which code fits your situation, the right code checker takes all your incomes. Only HMRC can issue a new code: updates go through your HMRC online account, as GOV.UK explains.