Why track income and expenses together?
Most free expense trackers only show you one side of the picture — what you've spent. But as a self-employed worker, the number that actually matters for your finances (and for HMRC) is profit: what's left after your business costs are deducted from what you've earned.
Tracking income alongside expenses means you always know your real trading position, not just your spending. This is especially useful for understanding whether your day rate or pricing actually covers your costs and leaves you a sustainable profit.
What counts as business income?
- Invoiced work — client invoices for project or contract work
- Retainers — recurring monthly or ongoing client payments
- One-off payments — single jobs, gig work, or ad-hoc projects
- Other business income — royalties, commissions, or anything else earned through self-employment
You should record income on the date it's received, not the date you raised the invoice — this matters for cash-basis accounting, which most sole traders use for Self Assessment.
How profit affects your tax bill
| Scenario | Income | Expenses | Taxable Profit |
|---|---|---|---|
| No expense tracking | £40,000 | £0 claimed | £40,000 |
| Rough estimate | £40,000 | £3,000 claimed | £37,000 |
| Properly tracked | £40,000 | £7,500 claimed | £32,500 |
The difference between a rough estimate and properly tracked expenses in this example is £4,500 of taxable profit — roughly £900 in tax at the basic rate, or £1,800 at the higher rate. Tracking income and expenses together makes it much easier to claim everything you're entitled to.
What is a Profit & Loss (P&L) report?
A P&L report (sometimes called an income statement) is a summary of your income, your costs, and the resulting profit over a set period — usually a tax year. It's one of the most useful documents you can hand to an accountant, because it shows the shape of your business at a glance rather than a long list of individual transactions.
A good P&L report breaks expenses down by category (so an accountant can see where the money goes — equipment, travel, subscriptions, etc.) and clearly states the final net profit figure that feeds into your Self Assessment.
Self Assessment and your profit figure
When you complete your Self Assessment tax return, you report your total income and total allowable expenses for the tax year (6 April to 5 April). HMRC then calculates your taxable profit and applies Income Tax and Class 4 National Insurance accordingly.
Having a running profit figure throughout the year — rather than reconstructing it in January — makes it far easier to budget for your tax bill and avoid surprises. It also means you can use our Tax Position calculator with real numbers instead of estimates.