Additional info sits under "Also needed for now" on your Home screen, below your five tasks. It is a few questions about things that go on the same return. You need to answer each one before you can submit, but a No is fine, and most people answer No to most of them.
Where to find it
On your Home screen, tap Additional info. The web address is app.taxpro.co.uk/claims/<your claim>/additional-info.
What we ask about
Pension tax relief: if you pay into a pension yourself, there may be relief to claim.
Gift Aid donations.
Child Benefit and other benefits in the household.
Marriage Allowance.
Student loan repayments taken from your pay.
Savings and other income: interest, dividends, rent or income from abroad.
Sold or gifted assets: property, shares or valuables worth more than £6,000.
Why it matters
Your return is filed once, so we collect these before you submit. Where your claim goes through Self Assessment, the return covers your whole tax position for the year, not just your expenses. Leaving out other income can mean HMRC query the return later, which delays your refund.
Some of it works in your favour too. Pension contributions and Gift Aid can increase your refund.
Your answers save as you go, and you can change any of them until you submit.
If you are not sure
Tell us roughly what the income or benefit is and we will tell you whether it needs declaring. Do not guess at figures. An approximate number you cannot back up is worse than asking.