Self Assessment deadlines for resellers

Why there are two deadlines

Most people only know about 31 January. But that's the date your return is due. Before you can file one, HMRC has to know you exist as a Self Assessment taxpayer — and telling them has its own, earlier deadline: 5 October after the tax year ends.

Miss it and HMRC can charge a failure to notify penalty. It's a percentage of the tax arising from the failure to notify — so if there's no tax due, there's no tax-based penalty to calculate. But if you do owe tax, delaying can make the penalty more costly. Telling HMRC yourself, before they ask, reduces it.

You generally only register once. If you're filing every year, you can ignore the October date and go straight to January — but if you registered before and then stopped filing, HMRC may need you to reactivate your Self Assessment account, so don't assume you're still on the system.

The January bill can be bigger than you expect

If you owe £1,000 or more, HMRC usually asks for payments on account — advance payments towards next year's bill, each one half of this year's. The first falls due on the same 31 January as the return itself.

So a first-time filer can face their whole first-year bill plus half of it again, on one day. It isn't an extra tax — it's paid forward, and it comes off next year — but it is a real cash-flow shock if nobody warned you. It doesn't apply if more than 80% of your tax was already collected through PAYE, which covers a lot of people with a day job.

Do I actually need to file?

The test is gross sales, not profit. If you took more than £1,000 across all your selling in a tax year — before deducting what you paid for the items, postage or fees — you generally need to report it, even if you barely made anything.

Selling your own unwanted clothes usually isn't trading at all. Buying things specifically to resell is. Check which side of the line you're on — it takes about a minute.