Capital Gains Tax when you sell: the 60-day trap

When does Capital Gains Tax apply?

Capital Gains Tax is the tax on the profit you make when you sell, or otherwise dispose of, an asset that's gone up in value. For landlords, that asset is usually a rental property.

You pay it on the gain, not the sale price. If you sell your own home, Private Residence Relief normally covers the gain, so there's nothing to pay. A rental you've never lived in gets no such cover, so the gain is taxable.

The trigger isn't the day you accept an offer or exchange contracts. It's completion: the day the sale finishes and the money changes hands. That's the date the clock runs from, and it catches people out because completion can land weeks after everything "felt" done.

The 60-day rule

Here's the part that trips landlords up. When you sell a UK residential property at a gain, you have to report it and pay the estimated tax within 60 days of completion. This goes on a separate return, the "Capital Gains Tax on UK property" return, filed through your HMRC online account. It does not wait for your annual Self Assessment.

So picture the clock. Completion is day zero. The solicitor sends the proceeds. You've sixty days, including weekends and bank holidays, to work out the gain, file the dedicated return, and pay HMRC. For a lot of landlords, the sale completes, the money is spent or reinvested, and the obligation surfaces only when the deadline has already gone.

You report the gain again later, on your Self Assessment for that tax year. What you paid within 60 days counts towards the final bill, so you're not taxed twice. The 60-day return is an upfront payment on account of Capital Gains Tax, not an extra tax.

How is the gain worked out?

Your gain is the difference between what you sell for and what the property cost you, with allowable costs taken off along the way. In plain terms:

• Start with the sale proceeds.

• Take off what you paid for the property.

• Take off the costs of buying and selling, such as legal fees, Stamp Duty paid on purchase, and estate agent fees.

• Take off the cost of capital improvements, such as an extension or a new kitchen where there wasn't one before. Ordinary repairs don't count here; those are allowable against your rental income instead.

What's left is your gain. You then deduct your tax-free allowance for the year, and the rest is taxed at the rate that applies to residential property.

A worked example

The numbers below are illustrative and rounded to keep the maths clear, not current figures.

Marcus bought a flat to let out for £200,000. She paid £8,000 in Stamp Duty and legal fees on the way in. A few years later she has a new kitchen and bathroom fitted, a genuine capital improvement, costing £20,000. She sells the flat for £300,000, paying £5,000 in estate agent and legal fees on the way out.

Her gain looks like this:

• Sale proceeds: £300,000

• Less purchase price: £200,000

• Less buying costs: £8,000

• Less capital improvements: £20,000

• Less selling costs: £5,000

• Gain before allowances: £67,000

From that £67,000, Marcus takes off her tax-free allowance for the year, and pays Capital Gains Tax on what's left at the residential property rate that matches her income. Because she's never lived in the flat, no Private Residence Relief applies. And because she sold at a gain, the 60-day clock started the day completion went through.

For help navigating Capital Gains, book a Capital Gains tax advice call.

What does it cost to miss the 60-day deadline?

Miss the 60-day window and HMRC can charge a late-filing penalty, then further penalties the longer the return stays outstanding. On top of that, interest runs on the tax you owe from the day it was due until the day you pay.

The maddening part is that none of it relates to whether you eventually declared the gain in your Self Assessment. You can file a perfect annual return and still be penalised, because the 60-day return is a separate obligation with its own deadline. The penalty is for being late on that return, full stop.

So the real risk isn't usually the tax itself. It's not knowing the obligation exists until the window has closed, then paying penalties and interest on top of a bill you'd have happily paid on time. The way to avoid it is to know the gain, the deadline and the likely tax before you complete, not after.

Once you've handled the sale, the gain still has to appear on your Self Assessment for that tax year. For how the rest of your property tax fits together, see tax on rental income. And if a deadline has already slipped, penalties and late filing explains what HMRC can charge and where there's room to appeal.