A property can have an attractive gross yield and still require cash from your salary each month. The mortgage is only one bill: empty weeks, management, repairs and Income Tax also absorb rent. This article works backwards from those bills to the rent you need.
The scenario covers one residential rental owned personally by one individual. It is not a company, portfolio or full tax-return calculation.
Three numbers that answer different questions
| Measure | What it tells you |
|---|---|
| Before-tax rent | What covers mortgage payments, running costs and your retained reserve, before Income Tax. |
| After-tax break-even rent | What leaves no average cash shortfall after estimated tax. |
| Rent for your chosen surplus | What also leaves the monthly amount you want to keep. |
These are advertised monthly rents during occupied periods. Empty weeks reduce the rent actually collected across the year. A break-even rent is a cost threshold, not a valuation of what the property will let for.
Build your rental scenario
The underlined figures are editable. Use local letting evidence, a mortgage quote and realistic annual costs. Other income means your own annual non-savings, non-dividend income before the Personal Allowance, after any relevant deductible pension contributions; exclude this property’s rent. Tax residence follows the landlord, not the location of the rental.
What happens at the rent you expect?
At £1,100.00 advertised rent and 2 empty weeks, annual receipts are £12,692.31. Deduct £2,469.23 of allowable running costs, £7,500.00 of mortgage payments, £600.00 retained for future work and £2,589.23 of additional Income Tax. That leaves -£466.15 for the year, or -£38.85 per month on average.
The monthly result averages the year. Repairs and tax payments will not arrive in equal monthly instalments. A positive average does not remove the need for a cash buffer, and this surplus is measured after the entered reserve has been set aside.
Why principal and interest are different
An interest-only mortgage keeps the initial balance outstanding throughout this first-year calculation. A repayment mortgage also pays down that balance: it usually needs more monthly cash, but part of the payment builds equity. Mortgage principal is not an allowable rental expense or a finance cost for the Section 24 reduction.
The £150,000.00 mortgage costs £625.00 a month. Over its first 12 payments, £7,500.00 is interest and £0.00 repays capital. Only the interest enters the Section 24 reduction; the full payment leaves your bank account.
Switching mortgage type holds the initial loan, rate and term constant. It compares the first year, rather than projecting a future refinancing rate or a sale price. A lender’s actual quote may have fees, payment timing or interest-only eligibility conditions this page does not include.
How Section 24 raises the rent threshold
For an individual residential landlord, mortgage interest does not reduce the property profit used to calculate Income Tax. Instead, qualifying finance costs can produce a basic-rate tax reduction. A higher-rate taxpayer can therefore pay tax even when very little cash is left after the mortgage.
The model adds positive property profit to your other income, applies the relevant tax bands and Personal Allowance taper, then subtracts the permitted finance-cost reduction. Tax on your other income alone is deducted to isolate the tax change associated with this rental.
Rent after allowable running costs produces £10,223.08 of taxable property profit before finance costs. Adding it to £55,000.00 of other income increases tax by £4,089.23 before the finance-cost reduction. The reduction is £1,500.00, leaving £2,589.23 of additional tax attributable to this scenario.
The reduction uses 20% of the smallest of first-year interest, positive property profit and income above the remaining Personal Allowance, capped at total Income Tax. £0.00 of interest is outside that base in this year; future use depends on the carry-forward rules and later income.
The reduction cannot generate a tax refund and is constrained by finance costs, property-business profits and adjusted total income above the Personal Allowance. In some low-rate Scottish cases the reduction can also lower tax on other income; a small negative additional-tax result reflects that effect. Unused relief is not counted as cash received today.
The monthly rent your plan needs
Before tax, £895.56 a month covers mortgage payments, running costs and the retained reserve. After tax, the zero-surplus threshold is £1,174.82. Your £0.00 monthly surplus target takes the required advertised rent to £1,174.82; collected annual rent at that point is £13,555.62.
A threshold you cannot charge is a warning about the deal. Compare similar properties with the same location, condition and tenancy terms. Keep the expected rent realistic; changing an input cannot create market demand.
The advertised monthly rent needs to be at least £1,174.82 to leave £0.00 a month after the entered costs and estimated tax. Your expected rent of £1,100.00 leaves -£38.85 a month.
Expenses paid now are different from money saved
Include actual allowable costs such as landlord insurance, service charges you pay, accountancy and qualifying repairs in annual running costs. Enter the agent’s percentage separately so it is not counted twice. Council Tax and utilities belong here only when you pay them.
An unspent reserve has not become a deductible expense. Improvements and mortgage capital repayments also do not become running-cost deductions merely because you paid cash. The separate reserve lowers the cash you can spend while leaving taxable profit unchanged. Move an amount into running costs only when it represents a qualifying expense in the modelled year.
Break-even cash flow is not lender approval
Lenders can test rental interest coverage using their own stress rates, coverage ratios, borrower circumstances and product rules. That test may pass while your actual after-tax cash flow is negative, or fail even when this calculation looks workable. Obtain a mortgage offer and confirm the lender’s treatment separately.
This page also leaves out acquisition taxes and fees, capital growth, sale costs and the opportunity cost of your deposit. Those matter for investment return even though they are not recurring monthly bills. Use the full Rental Yield Calculator for the wider deal; use the Section 24 calculator when comparing personal ownership with a company.
What the result means for the deal
The expected rent is £74.82 a month below the rent needed for your chosen surplus. Check comparable local lettings: if that higher rent is unrealistic, revisit the purchase price, mortgage or running costs. A higher assumed rent is not evidence that tenants will pay it.
A cheaper purchase or larger deposit reduces the loan while keeping rent unchanged in this scenario. Lower running costs or a lower quoted mortgage rate can also reduce the threshold. Check each change against evidence, including lease obligations, repair condition and the cash required for the purchase.
Methodology and scope
Collected rent allows for empty weeks. Cash flow deducts running costs, full mortgage payments, the retained reserve and estimated additional Income Tax. The required rent is the lowest monthly amount that meets your surplus target, rounded upwards to the penny.
This first-year model uses 2026/27 tax bands, the Personal Allowance taper and Section 24 limits for one individual owner and one residential rental. It excludes brought-forward losses or finance costs, other tax reliefs, savings and dividends, companies and non-resident cases. It is a planning estimate, not a full tax return or lender decision.