Why Use the Calculator?
You've been saving for a house. You've got pre-approval from a lender. But you still don't know: "How much should I actually spend?" A £250k house? £350k? £500k?
The calculator solves this by letting you test different scenarios instantly. Adjust your salary, deposit size, interest rate, and mortgage term to see what your monthly payment would be. No guessing, no rough "4.5× salary" math — real numbers based on lender-style calculations.
The 5-Step Walkthrough
Step 1
Enter Property Price
Start with the house you're interested in. Use the slider to adjust the price, or type in a specific value. The calculator will instantly update all results below.
Step 2
Set Your Deposit %
Enter how much you have saved as a percentage of the property price. 10% is common for first-time buyers. 20% is the "sweet spot" for getting the best rates. Drag the slider to see how deposit size affects your monthly payment and LTV (Loan-to-Value).
Step 3
Set Mortgage Term (Years)
Choose how long you want to pay back the mortgage. 25 years is typical in the UK. Shorter term = higher monthly payment but less total interest. Longer term = lower monthly payment but more interest paid overall.
Step 4
Set Interest Rate
Enter the annual interest rate (APR). You can toggle between UK Bank of England rates and US Federal Funds rates. The calculator updates with the latest rate as your baseline, but you can adjust it to test "what if rates were higher?"
Step 5
Review Your Results
The top shows your monthly payment. Below that: your Loan-to-Value (LTV) and total interest paid over the loan term. The split bar shows your deposit vs. loan visually.
5 Common Mistakes (& How to Avoid Them)
❌ Mistake 1
Forgetting Hidden Costs
The calculator shows your mortgage payment only. It doesn't include stamp duty (up to 15% on some properties), survey fees, legal fees, insurance, council tax, maintenance, or repairs. Budget 5–10% extra on top of the purchase price for these costs.
❌ Mistake 2
Using "4.5× Salary" as Your Budget
Just because a lender says you can borrow 4.5× your salary doesn't mean you should. This is a maximum, not a recommendation. If your budget is tight, you're one emergency (job loss, illness, rate rise) away from trouble. The calculator helps you test realistic affordability, not just maximums.
❌ Mistake 3
Not Testing Rate Changes
Interest rates will rise or fall. If you're buying with a variable rate, test what happens if rates jump +1% or +2%. Use the calculator to see your payment at different rate levels. If +2% makes it unaffordable, a fixed-rate mortgage might be safer.
❌ Mistake 4
Ignoring Maintenance Costs
Homeownership means unexpected repairs: boiler breaks, roof leaks, electrics fail. Budget 1–2% of the property value annually for maintenance. A £300k house = £3–6k/year maintenance buffer.
❌ Mistake 5
Comparing Yourself to Friends
"My friend afforded a £500k house on the same salary." Different friends have different situations: different deposits, different interest rates at different times, different other debts (car finance, student loans). Use the calculator to find YOUR number based on YOUR situation.
Pro Tips
💡 Tip 1: Test Deposit Scenarios
Adjust the deposit slider from 5% to 25% and watch how LTV changes. You'll see that jumping from 10% to 15% deposit unlocks better rates without a huge payment increase. Many buyers find the "sweet spot" between cost and rate improvement at 15%.
💡 Tip 2: Compare Term Lengths
Test 20-year vs. 25-year vs. 30-year terms. A longer term lowers monthly payment but increases total interest. The calculator shows both, so you can make an informed trade-off decision.
💡 Tip 3: Rate Stress-Test
After setting your scenario, increase the rate by 2% and note the new payment. If that payment would break your budget, you need either a lower purchase price, larger deposit, or longer term. This is the "stress test" lenders use.
💡 Tip 4: Save Scenarios
Write down your results for 2–3 price points (e.g., £250k, £300k, £350k) and share with a mortgage broker. They'll validate your numbers against their lender criteria.
Frequently Asked Questions
Q: Why does my bank say I can afford more than the calculator shows?
A: Banks use different assumptions. This calculator tests affordability strictly (payment alone). Banks also factor in your credit score, employment history, existing debts, and stress-test scenarios. The calculator is a rough guide; your bank's pre-approval is definitive.
Q: Should I use a 2-year or 5-year fixed rate?
A: Test both with the calculator. A 2-year fixed is typically 0.3–0.5% cheaper but renews sooner (risk of rates rising). A 5-year fixed is safer for planning but costs more upfront. Use the calculator to see the £/month difference and decide based on your risk tolerance.
Q: Can I afford a house if the calculator says no?
A: Maybe. If affordability is tight, explore: (1) Save a bigger deposit, (2) Extend the term, (3) Wait for rates to drop, (4) Buy a cheaper property, or (5) Improve income. The calculator helps you identify which lever to pull.
Q: How accurate is this calculator?
A: It calculates interest correctly, but it doesn't include insurance, stamp duty, or fees. Use it as a starting point, then consult a mortgage broker for exact figures before committing to an offer.