This is any money earned from paid work (overtime only counts if you work the hours regularly), self-employed profits or some benefits (such as contribution-based jobseeker's allowance or employment and support allowance, incapacity benefit – in some cases – or carer's allowance, but not child, housing, council tax or disability benefits).
It also includes any extra income above £300 you (or a partner) receive from a pension, savings, renting out a property, or things such as a trust or interest in the estate of a person who has died.
Also included is any income you received from the Coronavirus Job Retention Scheme (for instance, if you've been furloughed).
You don't need to include money paid for child maintenance or your children's income, and some maternity benefits are partly excluded – however, you could lose out on an average £495 if you don't deduct the right amount of maternity pay from your gross income.
For the self-employed, income is any profit made in the last tax year, as submitted on your tax return. If you haven't finished your tax return yet, make a best guess based on your profit so far. If your business is new and you've had no income from it in the last year, you can leave the income section empty.
If you've received one of the self-employed income support scheme grants because your business was impacted by coronavirus, you need to include details of this in your tax return / estimated profit.