Self-Assessment Payment Schedule Calculator UK

Use your accountant's projection, your bookkeeping profit to date, or a reasonable estimate. If you’re on a £50k profit at 20% income tax + Class 4 NI, your bill is roughly £10k–£11k. The number drives everything else in the calculation.

This determines your POA amounts. POA instalments are based on the prior year’s tax, not the current year. If you expect income to drop, you can apply to reduce POAs using form SA303 before each deadline.

This is the starting balance in your 18-month cashflow projection. Include any money already set aside for tax. The projection will show whether this reserve plus ongoing income will cover every HMRC payment as it falls due.

Monthly net self-employed income = what lands in your account after business expenses, before tax. Essential outgoings = non-negotiable monthly commitments (rent, mortgage, bills, food, transport). The gap is your monthly surplus available to build your tax reserve.

First year of self-employment triggers the double-payment calculation. POA exempt means your liability is under £1,000 or 80%+ collected at source via PAYE — if so, you only ever pay a balancing payment in January.

The payment schedule table lists every due date with the type (Balancing Payment, POA 1, POA 2), amount, and projected cash balance immediately after each payment. Negative balances are highlighted in red.

The line chart shows your projected closing cash balance each month. Highlighted dots (amber) are months when an HMRC payment falls due. The red dashed line is zero. Any month dipping below the line is a potential cash cliff.

If your income is expected to fall, the tool flags that you can reduce POAs via SA303. If any month turns negative, it flags Time to Pay and HMRC’s Payment Support Service number (0300 200 3822). Both banners link to the appropriate action.

In a non-first year, HMRC sets your POA amounts based on your prior year’s tax liability (not your estimated current-year liability). If last year you paid £8,000 in tax, your POA 1 is £4,000 (31 Jan) and POA 2 is £4,000 (31 Jul), totalling £8,000 paid on account. Your actual bill is settled the following January via a balancing payment (tax owed minus POAs already paid). If the POAs exceed your actual bill, HMRC refunds the overpayment.

Interest accrues from the day after the payment deadline at Bank of England base rate + 2.5% (currently 7.25% p.a.), compounding daily. Separate late payment surcharges apply: 5% of unpaid tax at 30 days overdue, another 5% at 6 months, another 5% at 12 months. Late filing penalties are separate: £100 immediately, then £10/day after 3 months (max £900), then 5% of tax owed at 6 months and 12 months. Penalties and interest can exceed the original bill for significant delays.

If you have a PAYE employer alongside self-employment, much of your tax is collected at source. If 80% or more of your total income tax for the year (including from self-employment) was already collected via PAYE, you are exempt from POA for that year. This is calculated automatically by HMRC when you file — but if you know your PAYE income is dominant, you can tick the "Exempt" option in this tool. For mixed-income earners, an accountant is recommended to confirm the split.

Self-Assessment POA applies to sole traders and partnerships (and directors who take dividends/salary above PAYE). Limited company Corporation Tax is due 9 months and 1 day after the end of the accounting period — no POA system. However, directors who draw dividends pay income tax on those via Self-Assessment, which does trigger POA if the dividend tax exceeds £1,000. Limited company owners should model both Corporation Tax timing and their personal SA bill separately.