Self Assessment Tax Calculator 2025/26
Frequently Asked Questions
When is the Self Assessment deadline?
Online filing deadline: 31 January. Paper return: 31 October. Payment deadline: 31 January (both balancing payment and 1st payment on account for next year). Late filing: £100 penalty immediately, increasing after 3 months.
What are payments on account?
If your SA tax bill exceeds £1,000 AND less than 80% was collected via PAYE, HMRC requires advance payments on account: 50% of last year's bill due 31 January, and 50% due 31 July. This can make your first January payment very large.
What is Class 4 National Insurance?
Self-employed people pay Class 4 NI: 9% on profits between £12,570 and £50,270, and 2% above £50,270 (2025/26). Class 2 NI was abolished from April 2024 — no longer a flat weekly charge.
Who needs to register for Self Assessment?
Register if: you're self-employed and earn over £1,000, a company director, earning over £100,000, have rental income over £1,000, or have untaxed income (foreign income, capital gains, etc.). Register by 5 October following the tax year.
Can I reduce my payments on account?
Yes — if you know your current year's income will be lower, apply to reduce payments on account via HMRC online or form SA303. If you reduce them too much, interest is charged on the underpayment.
What expenses can a sole trader deduct?
Allowable expenses: office costs, travel (not commuting), clothing (uniforms/protective), staff costs, advertising, professional subscriptions, phone/internet (business portion), stock, equipment (or capital allowances). Keep all receipts.
How do I pay my Self Assessment bill?
Pay online via HMRC's website using Faster Payments (up to £100,000), BACS, CHAPS, or debit/credit card. Your 10-digit Unique Taxpayer Reference (UTR) is needed. Allow time for payments to reach HMRC — pay several days before the deadline.
What if I can't pay my Self Assessment bill?
Contact HMRC before the deadline to set up a Time to Pay arrangement (spreading payments over up to 12 months). HMRC may agree to this for genuine hardship. Interest still accrues on unpaid amounts even with TTP.