Run the numbers before you talk to anyone.

Which calculator answers which question

Broadly they fall into three groups. How much can I borrow — the contractor calculator for day-rate income, and the retained profit calculator for directors who leave profit in the company. What will it cost — repayment, amortisation, rate change and overpayment. Does the deal work — LTV, BTL stress test, rental yield, stamp duty and debt consolidation.

Start with borrowing capacity if you are early in the process, and with cost if you already know roughly what you are buying.

What an estimate can and cannot tell you

These tools apply the standard methods lenders use, so the figures are a realistic starting point rather than a guess. What they cannot do is apply any individual lender's criteria — the multiple it uses, its minimum day rate, how much trading history it wants, or how it treats your particular income structure.

That is why two lenders can quote very different amounts on the same inputs, and why an estimate is a planning figure rather than an offer. Treat a calculator result as the question to take to an adviser, not the answer.

The two most useful for contractors

If you take a day rate, the contractor calculator shows what the 46-week annualisation method produces — usually a substantially larger figure than a high-street process working from your tax return would give you.

If you are a director leaving profit in the company, the retained profit calculator does something none of the others do: it sets the drawn-income basis most lenders use against the profit basis a specialist would apply, and shows the gap between them. For many directors that gap is the entire reason they were told they could not borrow enough.