Self Assessment tax calculator
Payments on Account often surprise filers in their second self-assessment year. The 31 January demand combines the prior-year balancing payment with the first 50% Payment on Account toward the new year, so the cash required can reach 150% of the headline tax figure. The system catches up again at 31 July with POA2.
This tool calculates your total liability, splits it into the balancing payment and POA instalments, and flags MTD for ITSA obligations if your qualifying income exceeds £50,000.
Your Tax Year
What this changes
Trading profit after expenses, capital allowances and any pension contribution. Drives both income tax (with PAYE and rental income stacked) and Class 4 NI at 6% / 2%. More than £50,000 of qualifying income brings MTD for ITSA into scope from 6 April 2026.
What this changes
Property rental profit after Section 24 mortgage-interest treatment, plus dividends or other untaxed income. Stacks above PAYE in the income tax bands, so combined with self-employment profit it can push you above £50,270 into the higher-rate band.
What this changes
Gross employment income from your P60. Income tax on this has already been collected at source and counts toward "tax already deducted", so increasing PAYE both adds tax due and adds tax already paid.
What this changes
Tax already paid through PAYE or other deductions at source. Subtracted from total liability to give the balancing payment due 31 January. If deducted tax covers more than 80% of your liability, payments on account are not triggered.
What this changes
Net contribution paid into a personal pension (the cash leaving your bank). HMRC adds 25% basic-rate uplift at source, so the gross figure widens your basic-rate band. Higher and additional-rate taxpayers claim the extra relief here, often turning a "balancing payment" into a refund.
What this changes
Plans 1, 2, 4 and 5 repay at 9% above the plan threshold. Postgraduate loans repay at 6%. The repayment is included in the balancing payment, but not in payments on account.
What this changes
CIS contractors deduct 20% from your labour invoices and pay it to HMRC. The deduction counts as tax already paid, so heavy CIS deductions often produce a refund rather than a balancing payment when your actual liability is lower.
Cash needed by 31 January 2028
Rates current for tax year 2026/27
These calculators are diagnostic tools intended to give you an initial estimate. They are not a substitute for personalised advice on your specific circumstances. Figures depend on the inputs you provide and on tax rules that change over time. Speak to us before acting on any result.
A CIMA Chartered Management Accountant will review your details and send you a tailored breakdown.
POA is triggered when Income Tax and Class 4 NI still due after tax deducted at source is at least £1,000, unless more than 80% was deducted at source. Student loan repayments are included in the balancing payment, not the POA figures. MTD for ITSA applies from 6 April 2026 to sole traders and landlords with qualifying income over £50,000.