UK Self Assessment late penalty calculator: what does filing late cost? Free, private

I missed the Self Assessment deadline. What will it cost?

Enter the tax year, the tax you owed, and the dates you filed and paid (or will). You get the late filing penalties, the late payment penalties, the interest, and what another 30, 60 or 90 days of delay would add.

A first read written from HMRC's published rules without a live lookup. Rules change; confirm the current text. Online returns due 31 January. Not tax advice.

Tax year of the return

Tax you owed for that year (£, zero if none)

Date you filed, or will file

Date you paid, or will pay

HMRC late payment interest rate (% a year, check GOV.UK)

Fill in the figures, then click Work out the cost.

Result

Penalties and interest

Ref	What	Amount

What waiting longer costs

If you file and pay this much later	Total penalties and interest	Extra

What you must do

Step	What it means

What it does, and what it leaves to you

Covers: the GBP 100, daily, 6-month and 12-month late filing penalties, the 5% late payment penalties at 30 days, 6 months and 12 months, simple daily interest, and a delay table.
Gives: an itemised penalty list, a total, and a checklist of what to do first.
Not decided: reasonable-excuse appeals, higher penalties for withholding information, paper returns, time to pay arrangements, interest on penalties, the Making Tax Digital points regime, and anything that changed after this was written.

Common questions

What is the penalty for filing a Self Assessment return late?

GBP 100 as soon as the return is a day late, even if you owe no tax. After three months, GBP 10 a day for up to 90 days (GBP 900). After six months, the greater of GBP 300 or 5% of the tax due, and the same again at twelve months.

What is the penalty for paying Self Assessment tax late?

5% of the unpaid tax once it is 30 days late, a further 5% at six months and a further 5% at twelve months. Interest also runs daily from the due date.

If I pay on time but file late, do I still get a penalty?

Yes. Filing and payment penalties are separate. A late return costs at least GBP 100 even if the tax was paid in full on 31 January.

What interest does HMRC charge on late Self Assessment tax?

Simple daily interest from the due date at HMRC's late payment rate, which moves with the Bank of England base rate. Enter the current rate from GOV.UK; this tool does not hard-code it.

Can I get a penalty cancelled?

If you had a reasonable excuse, such as serious illness, bereavement or a failure of HMRC's systems, you can appeal. Appeal within 30 days of the penalty notice. This tool does not decide whether an excuse is reasonable.

Is my data uploaded anywhere?

No. Everything is calculated in your browser and nothing is sent.