Plan your Self Assessment bill: income tax and Class 4 NIC on trading profit, payments on account (31 January / 31 July) and the balancing payment.
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Estimates the 2025/26 Self Assessment liability on self-employment profit — income tax (top-slice above any income already taxed at source) plus Class 4 NIC (6% between £12,570 and £50,270, 2% above; Class 2 abolished from 2024/25) — then builds the payment schedule: two payments on account of 50% of last year's bill and the balancing payment due the following 31 January.
£60,000 trading profit, £10,000 prior-year bill: income tax £11,432 + Class 4 NIC £2,456.60 = £13,888.60. Two £5,000 payments on account (31 Jan / 31 Jul), balancing payment £3,888.60, and next January's total due £10,832.90 including the first 2026/27 payment on account.
Enter your self-employment trading profit for the year.
Add any income already taxed at source (e.g. PAYE salary).
Enter last year's Self Assessment tax bill to compute the payments on account.
Read the schedule: 31 January, 31 July, and next January's balancing payment.
Last data update
July 5, 2026
Sources and references
HMRC — Understand your Self Assessment tax bill (gov.uk/understand-self-assessment-bill/payments-on-account); gov.uk/self-employed-national-insurance-rates; gov.uk/income-tax-rates.
The data in this calculator is updated regularly to reflect the latest official rates. When in doubt, consult the official sources listed above.
When your last Self Assessment bill was £1,000 or more and less than 80% of it was collected at source. Each payment is half of last year's bill, due 31 January and 31 July.
6% on profits between £12,570 and £50,270 and 2% above (2025/26). Class 2 NIC was abolished from April 2024.
HMRC refunds the overpayment (or sets it against your next bill) once the return is filed — the calculator shows the expected refund.