Your situation
Tax code with no P45
Independent site, not HMRC. Only HMRC can change your code: use your HMRC online account or app.
A missing P45 does not stop you starting work, but it changes the code on your first payslips.
Should come back to you
£930.60
In your January pay (month 10), if the new code reaches payroll by then.
| Tax on 1257L M1 | £930.60 |
| Tax with 1257L over the same pays | £0.00 |
| Tax line on that payslip | −£930.60 |
Assumes no other pay earlier in the tax year. With a P45 from an earlier job, the refund depends on the tax already paid there.
Without a P45, your new employer cannot see what you earned and paid since 6 April, so it asks you to fill in the starter checklist instead. If you had another job earlier in the tax year, you tick statement B and payroll uses 1257L on a month 1 or week 1 basis, an emergency code that gives each pay only one period of allowance. Lost P45s cannot be replaced (GOV.UK), but you can still ask the old employer to send one if they never did, and HMRC receives every employer's figures in any case. The cost of the emergency basis depends on gaps. Someone paid £2,600 a month in April and May, out of work until October, then back at the same pay, has £2,481.80 taken over the year on month 1, against £1,646.00 due. The difference, £835.80, normally comes back through payroll once HMRC sends a cumulative code, or after 5 April through a tax calculation letter.
Starter checklist: which code?
Code the employer uses
1257L M1
| Tax in the first month | £310.20 |
| Basis | month 1, until HMRC sends a code |
Rules read on HMRC’s texts by Radif Partners · Editorial policy · Method
Why a P45 matters to the new payroll
The P45 carries three things the new employer cannot guess: your code, your leaving date, and your pay and tax since the tax year began. With them, payroll continues a cumulative calculation, giving you the allowance for every month of the year so far and crediting the tax you already paid. Without them, it has to assume the worst about what came before. That is why GOV.UK warns that, with no P45, the tax taken in your new job might be wrong (your P45, P60 and P11D).
Three situations lead to the same place. Your old employer never issued one: ask them for it, since they should give it to you when you leave. It went missing: no copy can be made. Or this is your first job, or an extra job alongside another: there is no P45 to give. In each case you complete the starter checklist and the employer picks the code from the statement you tick.
What the emergency basis costs after a gap
With steady pay all year, month 1 and cumulative codes take almost the same tax each month. The difference shows when you spent months without income. Take £2,600 a month from an old job in April and May, nothing from June to September, then the same pay from October with no P45 and statement B ticked.
| Item | Income Tax |
|---|---|
| Old job, April and May, cumulative code | £620.60 |
| New job, October to March, 1257L M1 | £1,861.20 (£310.20 a month) |
| Total taken over the year | £2,481.80 |
| Tax due on the year's pay | £1,646.00 |
| Taken too much | £835.80 |
The four empty months each carried about a twelfth of the allowance, and the month 1 basis never lets the new payroll use it. On a cumulative code, the October payslip alone would have absorbed that unused allowance. Use the calculator at the top to try your own pay and start month; choose the X version when your pay dates vary from one period to the next.
Month 1 basis against cumulative
First pay, 1257L M1
£310.20
| First pay, 1257L cumulative | £0.00 |
| Difference on that pay | £310.20 |
| Free pay used by cumulative | £7,337.82 |
Cumulative counts the allowance of the months before the job started.
What comes back, and how
HMRC usually updates your code once it holds the details from both your new and your previous employer, which can take up to 35 days from your start date. The new code goes to you and to the employer, and if it shows you overpaid, the employer refunds the difference through your pay: on the next or the following payslip if you are paid monthly, on the third if weekly (GOV.UK). If the old employer's pay and tax figures are wrong, ask them for an amended P45; failing that, tell HMRC through the Check your Income Tax online service, which will contact the employer.
If the year ends before the code is fixed, HMRC reconciles the figures from every employer after 5 April and sends a P800 tax calculation or a Simple Assessment letter (overpayments and underpayments). A P800 refund claimed online arrives within 5 working days; a cheque sent automatically comes within 14 days of the letter.