Buy-to-let mortgage calculator
How much could you borrow? Buy-to-let lending is decided by the rent, not your salary — and the answer changes with the product you pick and how you borrow. Enter your figures once and see the loan every standard rule-set reaches, side by side, with the deposit each one implies.
The property
Pre-filled with a worked example — type over it with your own figures. Nothing you enter leaves your browser: no account, nothing saved.
Indicative borrowing range
At 125% interest coverage, across the standard rule-sets — arithmetic, not a lending decision.
The low end is a 2-year product limited by the rent test; the high end hits the 75% loan-to-value ceiling — on a 5-year fix the rent alone would support more than the ceiling allows.
Every standard rule-set, side by side
Rows outside your selected band are dimmed for comparison. ICRs, stress floors and LTV ceilings vary by lender — these are the standard shapes, and additional-rate borrowers, HMOs and multi-unit properties are often tested harder still.
| Rule-set | Rent tested at | Indicative max loan | Limited by | Deposit needed | Monthly payment |
|---|---|---|---|---|---|
5-year fixYour band Limited company / basic-rate | 125% × 4.50% | £225,000 | 75% LTV ceiling | £75,000 | £844 |
5-year fix Higher-rate taxpayer | 145% × 4.50% | £220,690 | Rent test | £79,310 | £828 |
2-year fix / trackerYour band Limited company / basic-rate | 125% × 6.50% | £177,231 | Rent test | £122,769 | £665 |
2-year fix / tracker Higher-rate taxpayer | 145% × 6.50% | £152,785 | Rent test | £147,215 | £573 |
Interest-only payments at your pay rate. The stressed rate is the higher notional rate the rent is tested against, not what you pay. Some lenders apply their own minimum stress rate even on 5-year products.
How lenders actually decide
Almost every buy-to-let lender starts from the same two checks. First the rent test: the annual rent must cover the mortgage interest by a margin — the interest coverage ratio — calculated at a stressed rate rather than the rate you'd pay. The maximum loan is annual rent ÷ (ICR × stressed rate). Second the loan-to-value ceiling: the loan can't exceed a set share of the property's value, typically 75%. Your indicative maximum is whichever limit is lower.
What most single-lender calculators hide is that the inputs to that formula are not fixed. The ICR is usually 125% for limited companies and basic-rate taxpayers but 145% for higher-rate taxpayers borrowing personally. The stressed rate is usually the pay rate plus 2% — with a floor around 5.5% — on products fixed for under five years, but the pay rate itself on most 5-year fixes (some lenders apply their own minimum even there). Move between those rule-sets and the same rent supports a very different loan. That spread is the point of this calculator: it is the difference between asking one lender and asking the market.
What it doesn't do
- It isn't any specific lender's criteria. Every lender sets its own ICRs, stress rates, floors and LTV ceilings — these are the standard shapes those criteria take, current as at August 2026, and individual lenders sit above and below them.
- It doesn't model top-slicing. Some lenders let surplus personal income make up a rent shortfall, which can lift the maximum beyond what the rent alone supports — a broker-placement question, not a formula.
- It ignores fees and tax: arrangement fees (often added to the loan), valuation and legal costs, and the stamp duty surcharge on additional properties all change what a purchase actually needs.
- It doesn't assess you. Lenders also weigh minimum income, landlord experience, portfolio size and property type — HMOs and multi-unit blocks are often tested harder — so a figure here is arithmetic, not a decision in principle.
- It is arithmetic, not advice. If the spread between rule-sets looks material for your position, that's the moment to speak to a specialist broker — not to pick a product.
Pricing the whole purchase? The stamp duty calculator prices the surcharge and the rental yield calculator tells you if the deal earns its keep — and if it's let room by room, the HMO mortgage calculator runs this same test on the room income. Remortgaging rather than buying? The BTL remortgage calculator runs payment and cash-released scenarios against your current position — or read how a BTL remortgage actually works and whether a limited company makes sense for your next purchase.
Common questions
- How much can I borrow for a buy-to-let mortgage?
- Buy-to-let borrowing is driven mainly by the rent, not your salary. Lenders take the annual rent and divide it by their interest coverage ratio multiplied by a stressed interest rate — so £1,200 a month tested at 125% coverage and a 5.5% stressed rate supports a loan of about £209,000. The loan is then capped at the lender's loan-to-value ceiling, typically 75% of the property's value. Whichever of the two limits is lower is your indicative maximum, which is what this calculator shows. Some lenders can also count surplus personal income ("top-slicing") where the rent falls short.
- Do you need a 25% deposit for a buy-to-let mortgage?
- Usually, yes. Most buy-to-let lenders cap the loan at 75% of the property's value, which means a 25% deposit; a few go to 80%. In practice the rent test can demand an even bigger deposit — if the rent doesn't support a 75% loan, the shortfall has to come from you. The calculator shows which of the two limits actually binds for your figures.
- How much rent do I need for a £200,000 buy-to-let mortgage?
- Tested at a 5.5% stressed rate, roughly £1,150 a month at 125% interest coverage (typical for limited companies and basic-rate taxpayers) or about £1,330 at 145% (typical for higher-rate taxpayers borrowing personally). A 5-year fixed product stressed at a lower pay rate needs less rent — which is one reason 5-year fixes are so common in buy-to-let.
- What is the interest coverage ratio and the stress rate?
- The interest coverage ratio (ICR) is how far the rent must exceed the mortgage interest — 125% is the regulatory minimum benchmark for the standard rent-based test at PRA-regulated lenders, and 145% is common for higher-rate taxpayers. The stress rate is the notional interest rate the test uses instead of your actual pay rate: typically the pay rate plus 2% (with a floor around 5.5%) on products fixed for under five years, and the pay rate itself on most 5-year-plus fixes.
- Why can I borrow more on a 5-year fix?
- Because the stress test is gentler. Products fixed for five years or more are typically tested at the pay rate itself — though some lenders apply their own floor even there — while shorter products are tested at the pay rate plus 2% or a floor of about 5.5%, whichever is higher. Testing the same rent at a lower rate supports a larger loan — the calculator shows the difference side by side.
- Do limited companies get better buy-to-let mortgages?
- Not cheaper — rates are often slightly higher — but the affordability test is usually kinder. Limited company applications are typically tested at 125% interest coverage rather than the 145% applied to higher-rate taxpayers borrowing personally, because the company pays corporation tax and full mortgage interest stays deductible. For a higher-rate taxpayer that difference alone can add tens of thousands to the maximum loan. Whether a company structure suits you at all is a tax question — take regulated tax advice before structuring a purchase around it.
This is one property. Your portfolio is the real picture.
Inside Primehold every property carries its live figures — value, loan, rate, rent — with the full dated history behind each one, scenario cards on every property, and a lender-ready export one click away. Built by Scott West, a practising specialist mortgage broker.