The salary you actually need
Most UK lenders apply an income multiple ceiling of 4.5x gross household income, with stretches to 5.0x or 5.5x where affordability and credit profile are particularly strong. Under the 4.5x base, a £300,000 mortgage requires combined gross income of around £66,700 — achievable as two earners on £33,000 each, or as a single applicant on £66,700.
That multiple is a cap, not a guarantee. The lender's affordability calculation looks at your committed outgoings — credit cards, loans, car finance, childcare, school fees, pension contributions — and works backwards from your net income to determine the maximum sustainable monthly mortgage payment. A household earning £75,000 with £600 a month of car finance and two children in childcare may actually have lower affordability headroom than a £65,000 household with no dependants and no debts.
Stretched multiples are available in three main scenarios. Professional schemes for newly qualified doctors, dentists, solicitors, accountants and pilots allow 5.0x–5.5x — bringing the required income down to around £55,000–£60,000. Higher earners (typically £75,000+ individual or £100,000+ joint) often access 5.0x–5.5x at standard high-street lenders based on income alone. And specialist affordability calculators (such as those at Nationwide, Halifax and Kensington) sometimes generate stretched outcomes when fixed outgoings are low.
What the monthly payment actually looks like
Monthly payments on a £300,000 capital and interest mortgage vary by rate and term. At a 4.50% fixed rate over a 25-year term, the monthly payment is approximately £1,667. At 5.00% it's £1,754, and at 5.50% £1,842. These are roughly the rate range available in mid-2026 across 2- and 5-year fixed products at 75%–85% LTV.
Extending the term reduces the monthly payment but increases total interest paid. A 30-year term at 4.50% drops the monthly to £1,520, saving £147 a month — but over the life of the mortgage you pay around £45,000 more in interest. Many buyers compromise by taking a 30-year term initially for cashflow flexibility, then making overpayments (most lenders permit 10% a year penalty-free) to shorten the effective term as income grows.
If you're on an interest-only mortgage, the £300,000 monthly cost is purely the interest: £1,125 at 4.50%, £1,250 at 5.00%. But you still owe £300,000 at the end of the term and need a credible repayment vehicle. Interest-only is rarely approved for residential cases without substantial equity, an investment portfolio or property sale plan to clear the capital.
Deposit thresholds that change the rate
Lenders price mortgages in LTV bands, and crossing into a lower band can save 0.30%–0.80% on the rate — a meaningful sum at £300,000. On a property valued at £375,000 with a £300,000 mortgage (80% LTV), you're in the most competitive bracket of the high-street market. Drop the mortgage to £262,500 (70% LTV) by adding £37,500 more deposit and you typically save another 0.10%–0.25% on rate.
The deposit thresholds that move the rate are typically 5%, 10%, 15%, 20%, 25%, 40% and 50%. The biggest single jump in pricing usually sits between 90% and 85% LTV — moving from a 10% to a 15% deposit. If you're close to a threshold, finding the extra £5,000–£10,000 can often save you more in rate over a 5-year fix than the deposit increase costs.
How stress tests interact with the £300k figure
Lenders stress-test affordability at a rate higher than the actual product — typically the reversion rate (SVR) plus 1.0%–3.0%, depending on the lender's model. In practice this means a £300,000 mortgage taken at 4.50% is assessed for affordability at a notional rate of 7.5%–9.0%, where the monthly payment would be approximately £2,219 to £2,520. Your household income must support these stressed figures, not the actual lower payment.
Stress tests are the most common reason borrowers feel their income multiple is being squeezed. The headline 4.5x multiple is the cap; the real ceiling is whatever the stressed affordability calculation outputs. For some lenders this is more generous than 4.5x; for others, particularly on shorter terms, it tightens to 4.0x or below.
Stamp duty and other up-front costs
On a £300,000 property purchase, stamp duty (SDLT in England and Northern Ireland) breaks down as: £0 for first-time buyers (full relief up to £300,000); £2,500 for home-movers (5% on the £50,000 above the £250,000 threshold); £17,500 for second-home or BTL purchases (5% surcharge across the whole price plus the standard band). Scotland (LBTT) and Wales (LTT) have different thresholds — check the current rates for your jurisdiction.
Add to that legal fees (£1,200–£1,800 typical), survey (£400–£1,200), mortgage product fees (£0–£1,999), valuation (often included or £200–£500), and broker fees if applicable (£0–£995). Total transaction costs on a £300,000 home for a home-mover sit in the £6,000–£9,000 range excluding stamp duty.
How to structure your application for the best outcome
Three structural decisions tend to matter most for a £300,000 borrower. First, the term: take the shortest term you can comfortably afford, because rate alone doesn't determine total cost. Second, the deposit: getting to the next LTV band materially changes pricing. Third, the lender choice: high-street lenders dominate vanilla cases, but if your income is partly self-employed, contract-based, bonus-heavy or includes rental income, specialist lenders often offer more generous affordability at near-identical rates.
A qualified broker is particularly valuable at the £300,000 mark because the income multiple, deposit threshold and affordability stress test combine in ways that aren't obvious. The same client profile can be declined by one lender and offered a £300k mortgage at a sharp rate by another with different criteria.
Your home may be repossessed if you do not keep up repayments on your mortgage. First Rung Now is not FCA authorised or regulated; we introduce consumers to FCA-regulated mortgage brokers. Nothing in this article is financial advice.