Buy-to-Let Mortgage Calculator
Investing in buy-to-let property requires different mortgage products with stricter lending criteria. Lenders typically require 125-145% rental coverage at stressed interest rates.
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A common mistake is calculating profit based on current low rates without stress-testing against higher rates. What looks profitable at 3% may become loss-making at 6%. Many landlords also forget the 5% additional stamp duty surcharge, letting agent fees, void periods, and tax changes that have reduced mortgage interest relief to basic rate only.
Understanding true buy-to-let profitability requires looking beyond headline rental yield. Enter your property details below to calculate your mortgage costs, rental coverage ratio, and whether your investment passes lender stress tests.
Property & Mortgage Details
LTV: 0% (most BTL lenders cap at 75%)
Gross Rental Yield
0%
Annual rent ÷ property value
Profitability Analysis
Monthly Interest-Only Payment
£0
£0 per year
Monthly Cash Flow
+£0
Rent £1,200 − Mortgage £0
Interest Coverage Ratio
0x
Below requirement
Annual Surplus
+£0
Before tax & costs
Lender Stress Test
At 0% stress test rate:
£0/mo
ICR: 0x
May not pass
Over 25 Years
Total Interest Paid
£0
Capital Owed
£187,500
With interest-only, you still owe the full mortgage at term end
Understanding Buy-to-Let Mortgages
Buy-to-let (BTL) mortgages work differently from residential mortgages. Most are interest-only, assessed on rental income rather than personal earnings, and come with stricter stress testing requirements.
Why Most BTL Mortgages Are Interest-Only
Advantages
- • Much lower monthly payments
- • Better monthly cash flow
- • More properties affordable on same income
- • Tax efficiency (interest is deductible cost)
- • Flexibility to invest surplus elsewhere
Risks
- • Debt never reduces
- • Reliant on property value for exit
- • Vulnerable to rate increases
- • Must have repayment strategy
- • Negative equity risk if prices fall
Lender Stress Testing & ICR Rules
Lenders don't just check if rent covers your mortgage now—they stress test against higher rates to ensure you can survive rate rises:
Basic Rate Taxpayers
ICR typically 125% at 5.5% stress rate
£1,000 payment needs £1,250 rent
Higher Rate Taxpayers
ICR typically 145% at 5.5% stress rate
£1,000 payment needs £1,450 rent
This is why many properties that look profitable on paper fail lender tests—the rent might cover your actual rate, but not the stressed rate.
The Risk of Relying on Property Sale
Warning: Many landlords plan to sell the property to repay the mortgage. This works if property values rise, but if prices fall or stagnate, you could be trapped—unable to sell for enough to clear the debt, but also unable to afford repayments if rates rise. This is especially risky for those who bought at market peaks.
Best Case
Property rises 30% over 25 years. Sell for £325k, repay £187k mortgage, pocket £138k profit (minus CGT).
Break Even
Property value unchanged. Sell for £250k, repay £187k mortgage, £63k deposit returned (no real profit after costs).
Worst Case
Property falls 20%. Sell for £200k, still owe £187k + fees. Barely cover debt, lose deposit.
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