Most people think of their tax return as something their accountant handles once a year, with information flowing one way. In reality, the return is only as accurate as what you tell them. There are a handful of things that are easy to forget, or that people simply don’t realise need mentioning at all, and missing them can cause real problems further down the line.

Here’s what’s often overlooked, and why it’s worth getting ahead of it before your 2025/26 return is prepared.

Selling a residential property

If you’ve sold a residential property that isn’t your main home, there’s a 60-day window from completion to report the disposal and pay any capital gains tax owed. This is a separate process to your self-assessment return, and it runs on its own clock.

The issue is timing. If you don’t tell your accountant as soon as the sale completes, that 60-day window can close before they’ve even had the chance to act. Missing it can mean penalties and interest, on top of whatever tax is due. As soon as a residential property disposal is on the horizon, or has happened, get in touch straight away rather than waiting until your usual tax return conversation.

Every source of income, not just the obvious ones

Self assessment isn’t only about your salary or your business profits. HMRC expects to see the full picture, and that includes income you might not think to mention.

This covers dividends, investment income, capital gains, and certain gifts. Some of these have their own allowances and rules, and your accountant can only apply them correctly if they know the income exists. Leaving something out isn’t usually deliberate; it’s just that people don’t always realise it counts as reportable income in the first place.

The safest approach is to tell your accountant about anything that’s come in over the year, even if you’re not sure whether it’s relevant. It’s easier for them to rule something out than to find out about it after the return has already been filed.

Losses count too

It’s not just profits and gains that matter. If your investments have lost money over the year, that’s worth mentioning as well.

Losses can often be offset against gains elsewhere, which may reduce the amount of tax you owe. Some losses can also be carried forward to future years. None of that can happen if your accountant doesn’t know about them, so treat a bad year for your investments the same way you’d treat a good one, and pass on the details.

Furnished holiday lets

The tax treatment of furnished holiday lets changed for the 2025/26 tax year. They’re no longer treated as a business in the way they were previously, which affects things like capital allowances and pension contributions.

There is a practical upside. Losses from a furnished holiday let can now be offset against your other rental income, which wasn’t previously the case. If you own a furnished holiday let, this is worth raising with your accountant directly, as it’s a change that can genuinely work in your favour if it’s accounted for correctly.

A simple checklist

Before your 2025/26 return is prepared, it’s worth running through the following:

  • Have you sold a residential property that isn’t your main home?
  • Have you received dividends, investment income, capital gains, or significant gifts this year?
  • Have any of your investments lost value?
  • Do you own a furnished holiday let?

If the answer to any of these is yes, make sure your accountant has that information before your return is submitted.

If you’re unsure whether any of this applies to you, or you’d like to talk through your position ahead of the 2025/26 filing season, we’re happy to help. Call us on 01472 357125 or contact us through the website.