4.0% / 25 yrs
£1,584
per month
4.5% / 25 yrs
£1,667
per month
5.0% / 25 yrs
£1,754
per month
6.0% / 25 yrs
£1,933
per month
A £300,000 mortgage is the reality for a large proportion of buyers in the South East, East of England, and outer London — areas where even a modest three-bedroom home regularly requires this level of borrowing. At this loan size, every decision carries more financial weight. A 0.5% difference in interest rate moves your monthly payment by around £85, and costs or saves approximately £25,500 over 25 years.
Choosing between a 25-year and 30-year term saves roughly £200 per month but costs an extra £73,000 in total interest at 4.5%. On a £300k mortgage, the difference between a sharp financial decision and a passive one — renewing on time, choosing the right term, hitting a better LTV tier — compounds into sums that materially change what you have available in retirement.
£300,000 Mortgage Calculator
£300k mortgage repayment comparison table
Note how the 20-year term at 4.5% costs £397 more per month than the 35-year term — but saves £118,800 in total interest. At £300k that saving is not trivial; it is the equivalent of a substantial pension contribution or property improvement fund.
| Interest rate | 20-year term | 25-year term | 30-year term | 35-year term |
|---|---|---|---|---|
| 3.5% | £1,739 | £1,502 | £1,347 | £1,243 |
| 4.0% | £1,818 | £1,584 | £1,432 | £1,330 |
| 4.5% | £1,898 | £1,667 | £1,520 | £1,421 |
| 5.0% | £1,980 | £1,754 | £1,610 | £1,514 |
| 5.5% | £2,063 | £1,841 | £1,703 | £1,610 |
| 6.0% | £2,149 | £1,933 | £1,799 | £1,708 |
| 6.5% | £2,237 | £2,027 | £1,897 | £1,809 |
Estimates only. Capital repayment mortgage. Fees and insurance not included.
Term length versus total cost — the £300k trade-off in full
At £300,000 the term length decision has a larger absolute impact than at any lower loan size. The four cards below show exactly what each common term costs monthly and in total at 4.5% — the 20-year term is cheapest overall, though it demands the highest monthly commitment.
20-year term
£1,898/mo
Total: £455,600
Interest: £155,600
25-year term
£1,667/mo
Total: £500,100
Interest: £200,100
30-year term
£1,520/mo
Total: £547,200
Interest: £247,200
35-year term
£1,421/mo
Total: £596,820
Interest: £296,820
The difference in total interest between a 20-year and 35-year term on £300k at 4.5% is £141,220 — nearly half the original loan amount, paid purely in additional interest. The monthly saving of £477 from choosing the 35-year term over the 20-year term costs almost £300,000 extra in interest over the full period.
If affordability forces a longer term, overpaying is the answer. Even £200/month extra on a 30-year term at 4.5% saves approximately £39,000 in interest and cuts around five and a half years off the term. For a detailed breakdown, see our guide on whether to overpay your mortgage.
How the monthly payment on a £300k mortgage is calculated
The standard amortisation formula underpins every mortgage repayment calculation in the UK, regardless of lender. Understanding it — even at a surface level — helps you verify figures independently and model different scenarios with confidence.
Standard amortisation formula
M = P × [ r(1 + r)ⁿ ] ÷ [ (1 + r)ⁿ − 1 ]M = monthly payment
P = principal (£300,000)
r = monthly interest rate = annual rate ÷ 12
n = total payments = years × 12
Worked example: £300,000 at 4.5% over 25 years
- r = 4.5% ÷ 12 = 0.375% = 0.00375 per month
- n = 25 × 12 = 300 payments
- M = 300,000 × [0.00375 × (1.00375)³⁰⁰] ÷ [(1.00375)³⁰⁰ − 1]
- M ≈ £1,667 per month
In the opening month, approximately £1,125 covers interest and only £542 reduces the capital balance. The crossover point — where more of each payment goes to capital than interest — arrives at around month 174 (year 14.5). This is why large overpayments in the first decade have a disproportionate impact.
For an interest-only mortgage at the same rate: (£300,000 × 4.5%) ÷ 12 = £1,125 per month. That is £542 less per month — but the full £300,000 remains outstanding at the end of the term. At £300k, the capital risk of an unplanned interest-only mortgage is substantial. See our repayment vs interest-only guide for a full comparison.
Overpayment impact at £300,000
At this loan size, the financial return from overpaying is more compelling than at lower amounts — because the interest saving is calculated on a larger base. The table below shows what different monthly overpayment amounts save on a £300,000 mortgage at 4.5% over 25 years.
Overpayment savings — £300,000 at 4.5% over 25 years
| Overpay £100/month | Saves ~£20,500 interest, cuts ~2.5 years |
| Overpay £200/month | Saves ~£39,000 interest, cuts ~4.5 years |
| Overpay £300/month | Saves ~£55,500 interest, cuts ~6 years |
| Overpay £500/month | Saves ~£83,000 interest, cuts ~9 years |
An overpayment of £200/month on a £300k mortgage saves £39,000 in interest — at an effective guaranteed return equal to your mortgage rate, completely tax-free. Most lenders allow up to 10% of the outstanding balance per year without an early repayment charge — on £300k that is up to £30,000 per year in penalty-free overpayments.
Real UK buyer scenarios at £300,000
Rachel and Ben are upsizing in Guildford, Surrey. They are selling their flat for £285,000 — after clearing their existing £140,000 mortgage and estate agent costs, they net roughly £138,000 in equity. They use £75,000 as a 20% deposit on a £375,000 purchase, keeping the remainder as an emergency fund, giving them a new mortgage of £300,000 at 80% LTV.
Their 80% LTV position unlocks a five-year fix at 4.15% over 25 years. Monthly repayment: approximately £1,612. Their combined income is £98,000, so the mortgage represents around 33% of their combined net monthly take-home — comfortable, with room for the rate to rise at renewal without straining their budget.
Stamp duty on £375,000 as home movers: £8,750. They budget a further £3,000 for solicitor and survey fees. Total upfront costs excluding deposit: approximately £11,750.
Dr. Priya is a GP earning £72,000 and buying solo in Cambridge for £333,000. With a 10% deposit of £33,300 she needs a £299,700 mortgage — effectively £300k. At standard 4.5× income her maximum borrowing is £324,000, so £300k is well within range. However, as a doctor she qualifies for a professional mortgage product at 5× income, giving her additional headroom.
She secures a two-year fix at 4.55% over 25 years. Monthly repayment: approximately £1,677. Her take-home is roughly £4,350/month after tax. The mortgage represents 38.5% of net income — workable but close to the upper comfort threshold. She sets up a £150/month overpayment from day one and plans to remortgage to a five-year fix at the end of the two-year period.
David and Claire took out a £340,000 mortgage six years ago. Their outstanding balance is £303,000 with 19 years left. Their fixed rate expired last month and their lender's SVR is 7.49%. Their monthly payment has jumped from £1,590 to £2,417 — an increase of £827 per month.
They find a new five-year fix at 4.45%. New monthly payment over 19 remaining years: approximately £1,937. Monthly saving versus SVR: £480. Over the five-year fixed period that is £28,800 saved before accounting for the £1,499 arrangement fee on the new deal.
They also check their stamp duty position — no additional stamp duty applies to a straight remortgage on the same property.
What salary do you need for a £300,000 mortgage?
A £300,000 mortgage sits above the reach of the average single UK income at standard lending multiples. Understanding exactly where you sit — and what options exist if you fall short — is important before applying.
| Income scenario | 4× multiple | 4.5× multiple | £300k mortgage |
|---|---|---|---|
| £55,000 solo | £220,000 | £247,500 | Below threshold |
| £60,000 solo | £240,000 | £270,000 | Needs specialist lender |
| £67,000 solo | £268,000 | £301,500 | Achievable at 4.5× |
| £75,000 solo | £300,000 | £337,500 | Comfortable at 4× |
| £40,000 + £35,000 jt | £300,000 | £337,500 | Achievable jointly |
| £45,000 + £40,000 jt | £340,000 | £382,500 | Comfortably within reach |
| £60,000 + £25,000 jt | £340,000 | £382,500 | Comfortably within reach |
Income multiples are illustrative. Final decisions depend on outgoings, credit history, deposit size, and employment type.
For sole applicants falling short of the standard thresholds, professional mortgage lenders — catering specifically to doctors, solicitors, chartered accountants, and engineers — typically offer 5× or 5.5× income multiples. At 5×, a salary of £60,000 supports a £300,000 mortgage. A whole-of-market broker is best placed to find the right lender for your specific profile without scattering hard searches across multiple applications.
When is this calculator most useful?
🏘️
Buying in the South East
£300k is a realistic borrowing figure for average-priced properties across much of Kent, Essex, Hertfordshire, and outer Surrey. Use this to set a firm monthly budget before viewing.
📐
Choosing between term lengths
At £300k the total interest difference between a 20 and 35-year term is over £140,000. The term grid above makes the trade-off visible before you commit to a figure with your lender.
🔄
Remortgage shock-check
Enter your current balance and compare SVR versus a new fixed deal. At £300k even a few months on the SVR costs thousands — know your numbers before your deal ends.
💰
Modelling deposit size impact
Compare 10% versus 15% or 20% LTV at this loan size. The rate saving at each tier is worth hundreds per month and tens of thousands over the term.
Common mistakes on a £300,000 mortgage
Treating the 35-year term as a permanent arrangement
Taking a 35-year term for maximum affordability is a legitimate short-term strategy — but it only makes financial sense if you shorten the effective term through overpayments. At £300k, allowing a 35-year term to run to completion costs £141,000 more in interest than a 20-year term. If you take a longer term, set a firm overpayment target from month one.
Underestimating stamp duty on South East properties
At this borrowing level you are likely purchasing in the £330,000–£400,000 range. Home movers face stamp duty of approximately £4,000–£7,500 on properties in that bracket. First-time buyers pay 0% up to £300,000 and 5% above that, so they typically pay £1,500–£5,000 in the same bracket — but stamp duty is still often the most expensive single transaction cost, more than solicitor and survey fees combined.
Stretching to maximum borrowing without a rate-rise buffer
On £300k, a 1% rate increase at renewal adds approximately £168/month. If your monthly budget is already tight at your current rate, a 1% rise at the next fixed deal could cause real financial difficulty. Build at least £150–£200/month of headroom into your budget before completing, and consider a five-year fix for greater certainty at this loan size.
Not checking whether a joint application affects both parties equally
A £300,000 joint mortgage is a significant long-term financial commitment for both applicants. If the relationship breaks down, both parties remain legally liable for the full debt until the mortgage is formally reassigned or the property sold. Seek independent legal advice on joint mortgage implications — not just the affordability calculation — before applying.
Forgetting that arrangement fees add to the total cost
A mortgage with a £999 arrangement fee on a rate of 4.35% may work out more expensive than a fee-free deal at 4.55% — depending on the loan size and how long you hold the product. On £300k, always calculate the total cost over the fixed period (monthly saving × months) versus the arrangement fee before choosing between fee and fee-free products.
Frequently asked questions
What is the monthly payment on a £300,000 mortgage?
At 4.5% over 25 years on a capital repayment basis, monthly payments are approximately £1,667. At 5% the figure rises to £1,754, and at 6% to £1,933. Adjusting the term moves the payment considerably — at 4.5% over 30 years the monthly cost drops to £1,520, while over 20 years it rises to £1,898.
What salary do I need for a £300,000 mortgage in the UK?
At 4.5× income you need to earn at least £66,667 gross per year as a sole applicant. At 4× the threshold rises to £75,000. For joint applicants, combined salaries of £70,000 (e.g. £40k + £30k) comfortably meet most lenders' criteria. Professional mortgage products at 5× income reduce the solo threshold to £60,000.
How much deposit do I need for a £300,000 mortgage?
Borrowing £300,000 on a £333,333 property requires a 10% deposit of £33,333. A 5% deposit (on a £315,789 property) requires £15,789 and is the minimum accepted by most lenders. At this loan size, the monthly payment difference between 90% and 85% LTV is approximately £100, making saving the extra deposit meaningful.
How much total interest do you pay on a £300,000 mortgage?
At 4.5% over 25 years you pay approximately £200,100 in interest on top of the £300,000 borrowed — a total of around £500,100. Over 30 years total interest rises to £247,200. Over 35 years it reaches £296,820. Overpaying £200/month from the outset saves roughly £39,000 in interest and cuts around four and a half years off a 25-year term.
Where in the UK is a £300,000 mortgage most common?
A £300,000 mortgage is most typical in the South East, East of England, and outer London, where average property prices regularly require this level of borrowing for a standard three or four-bedroom home. It is increasingly common in commuter belt areas of the South West and East Midlands, and for higher-value properties in major northern cities.
Related calculators and guides
Mortgage
£250k mortgage monthly payment
Compare repayments at a slightly lower loan amount with the same tools.
Property
Stamp duty calculator
At this price range, stamp duty is a significant upfront cost — calculate it before making an offer.
Guide
Should I overpay my mortgage?
At £300k the interest saving from overpaying is substantial — find out when it makes sense.
DisclaimerAll figures are estimates for illustrative purposes only and do not constitute financial or mortgage advice. Monthly repayments will vary based on your lender's specific terms, associated fees, and changes in interest rates. Always speak to a qualified, FCA-regulated mortgage adviser before making any borrowing decision.
About the author
✓ Editorially reviewed — all Poqet guides are checked for factual accuracy before publication and updated when UK rates or legislation change. Editorial Policy