Mid-Year Job Change Tax Calculator, 2026/27

How this is calculated

This calculator compares two figures: the tax that is actually due for the year on combined earnings from both jobs, using the standard income tax bands, against the tax likely to be deducted by a new employer operating an emergency, non-cumulative tax code before HMRC issues the correct code.

A non-cumulative code taxes each payment as if it were the only income received in that period, ignoring earnings already received from the previous employer, which usually results in the new employer under-deducting tax initially, since it effectively gives the employee a fresh slice of tax-free personal allowance.

Once a P45 is provided, or HMRC issues an updated tax code based on its records, the new employer switches to a cumulative basis that gradually corrects any past under- or overpayment through subsequent payslips for the remainder of the tax year.

Why job changes commonly trigger the wrong tax code

The most common trigger is a delay or failure to provide the new employer with a P45 from the previous job, which forces HMRC's default emergency code, usually the standard personal allowance applied non-cumulatively, until the new employer receives better information.

Directors moving income between their own company and outside employment, or between two companies they run, should be especially careful, since HMRC systems can be slower to reconcile multiple sources of PAYE income for a single person within a tax year.

What to do if the numbers do not match your payslip

If a payslip shows a materially different tax deduction from the estimate here, check the tax code shown against your latest HMRC tax code notice, and confirm whether it is being applied on a cumulative or a Week 1/Month 1 (non-cumulative) basis, which is usually indicated next to the code.

Persistent discrepancies after two or three payslips in the new job are worth raising directly with HMRC or a payroll adviser, since correcting a code promptly avoids a larger one-off adjustment, or an unexpected tax bill, later in the year.

Why was I taxed more in my first payslip after changing jobs?

Most likely your new employer applied an emergency tax code on a non-cumulative basis because they had not yet received your P45 or an HMRC tax code notice, which can result in incorrect deductions until it is corrected.

Will HMRC automatically fix an emergency tax overpayment?

Usually yes, once HMRC issues the correct cumulative tax code to your new employer, subsequent payslips in the same tax year normally adjust for any earlier over- or under-deduction automatically.

Does a P45 matter if I am moving into my own limited company?

Yes. Even when moving to a company you own and control, PAYE rules still require a P45 or a starter checklist so the correct tax code can be applied from your first payslip.

What if the tax year ends before the correction happens?

If the discrepancy is not corrected by 5 April, it should resolve when HMRC reconciles your total income for the year, potentially resulting in a tax refund or an underpayment notice through your tax code the following year.