Which number gets assessed
An employee hands over a payslip and the assessable income is obvious. For the self-employed there are at least four candidate numbers, and lenders use the smallest one.
| Figure | What it is | Used by lenders? |
|---|---|---|
| Revenue / turnover | Everything invoiced | No. Ignored entirely. |
| Gross profit | Revenue less direct costs | No. |
| Net profit before tax | After all business expenses | Yes — this is the starting point. |
| Net profit after tax | What actually reaches you | Often the basis for affordability, depending on jurisdiction. |
This is the single biggest source of disappointment. Someone invoicing £120,000 a year thinks of themselves as earning £120,000. After £25,000 of legitimate expenses the assessed figure is £95,000 — and the tax reduction they worked hard with their accountant to achieve is the very thing that shrinks their borrowing capacity.
Minimising taxable profit and maximising borrowing power are directly opposed goals. If a mortgage application is coming in the next two years, that is a conversation to have with your accountant before the accounts are finalised, not after. Aggressive expensing in the two assessment years can cost you far more in borrowing capacity than it saves in tax.
Averaging, and why growth works against you
Most lenders want two to three years of accounts and will use an average. Some use the most recent year if it is lower. Very few will use the most recent year if it is higher.
For a business growing quickly, that asymmetry is expensive:
| Year | Net profit |
|---|---|
| Two years ago | 42,000 |
| Last year | 61,000 |
| Average used | 51,500 |
You are earning 61,000 and being assessed on 51,500 — about 16% less. If the trend reverses, the same lender will use the lower year rather than the average, so the rule works against you in both directions. That is not unfairness so much as the price of income that genuinely is less predictable than a salary.
Two practical consequences. A strong recent year does not fully count until it has a peer, which is an argument for waiting one more filing before applying if the trend is steep. And if your business is seasonal or lumpy, the averaging is doing something closer to the right thing than it feels like — see reserving tax on irregular income for the cash-flow side of the same problem.
Add-backs: the money you can argue back
Some costs reduce accounting profit without reducing the cash actually available to you. Lenders will often add these back to the assessed income — but almost never automatically. You or your broker have to identify them and evidence them.
- Depreciation. A non-cash charge. Very commonly accepted, and often the largest single add-back.
- One-off expenses. A genuinely non-recurring cost — a legal dispute, a relocation, an equipment purchase — can be argued back with evidence that it will not repeat.
- Director's pension contributions. Frequently added back, on the basis that they are discretionary and could be reduced.
- Interest on debts being repaid. If a business loan is being cleared as part of the transaction, its interest may be added back.
- Retained profit in a company. Some lenders will consider profit retained in the business rather than only salary and dividends drawn. This varies enormously between lenders and is often the difference between two very different offers.
The last two are where a broker who knows the market earns their fee. Add-back policy is not published, differs sharply between lenders, and is the main reason two applications on the same accounts can return offers tens of thousands apart.
Worked example: revenue vs. assessable income
A consultant, two years trading
| Line | Year 1 | Year 2 |
|---|---|---|
| Revenue | 96,000 | 124,000 |
| Business expenses | −21,000 | −28,000 |
| Depreciation (non-cash) | −4,000 | −4,000 |
| Net profit | 71,000 | 92,000 |
Without add-backs. Average of 71,000 and 92,000 = 81,500 assessed.
With depreciation added back. 75,000 and 96,000, averaged = 85,500.
That 4,000 difference in assessed income is worth roughly 20,000–30,000 of additional borrowing capacity at typical assessment rates — from one line item that nobody would have added back unless it was pointed out.
And note the headline gap: revenue of 124,000 in the latest year, assessed income of 85,500. The applicant thinks of themselves as a 124,000 earner. The lender is working with a number 31% lower.
Sole trader, company, or partnership
Business structure changes which documents are requested and which figure is read.
- Sole trader. Simplest. Tax returns and the accompanying computations; net profit is the figure. Two to three years typically required.
- Partnership. Your share of net profit, evidenced by the partnership accounts and your own returns.
- Limited company. The most variable. Many lenders count only salary plus dividends drawn — which penalises directors who leave profit in the business for sensible reasons. Others will assess salary plus a share of retained profit. Finding a lender in the second group is often worth more than anything else in the application.
Whichever applies, expect to provide accountant-prepared accounts, tax returns and computations, and typically three to six months of business and personal bank statements. Lenders read those statements: regular gambling transactions, frequent buy-now-pay-later use and returned direct debits all cause real problems, and the review window is short enough to be worth waiting out.
Preparing two years ahead
- Tell your accountant a mortgage is coming. The single highest-value action. It changes how aggressively they minimise profit in the assessment years.
- Reduce unused credit limits. Free, fast, and usually the largest single gain — an unused card limit is assessed as a monthly commitment at 3–3.8% of the limit. Do it months ahead so it shows on your file.
- Reserve tax as you earn it. Unpaid tax is assessed as the liability it is, and a visibly provisioned reserve is a far better look than an unexplained future claim on your income.
- Clear short-term debt. A loan with 18 months left is counted at its full monthly cost; clearing it converts that whole payment into borrowing capacity.
- Keep business and personal separate. Mixed accounts make the assessment harder, slower and more conservative.
- File on time. Late filings limit which lenders will look at you at all.
What this cannot tell you
- Policy varies enormously between lenders — years of accounts required, add-backs accepted, treatment of retained profit, and how recently you must have started trading. Two applications on identical accounts can differ by six figures.
- Rules change. Affordability requirements are set by regulators and lender policy, both revised regularly. Anything here describes mechanisms, not current policy.
- Affordability is one test of several. Credit history, deposit size, the property itself and the loan-to-value band all sit alongside it, and any of them can decline an application that passes affordability comfortably.
- A broker is genuinely worth it here. This is the one lending situation where knowing which lender to approach changes the outcome more than anything the applicant can do alone.
For the mechanics of the affordability test itself — the stressed rate, the living-cost floor and how credit limits are counted — see what a lender will actually lend you.