Can I Afford This House? Sanity Check
Run a UK house purchase through the 50/30/20 rule and stress test the mortgage against ±10pp interest rate moves. Set against 100 years of Bank of England base rate history so you can see how common today's rate actually is.
Your numbers
LTV: 90.0%
The headline fixed-rate quote. The stress test below shows what happens if rates move ±10 percentage points.
Combined gross salary for the household. Used to estimate take-home pay and the share of net income the mortgage will consume.
What happens to my data?
Mortgage size
£270,000
£30,000 deposit
Monthly payment
£1,501
39.7% of net income (Risky)
Recommended buffer
£673/mo
Extra cushion to survive a +4pp rate shock when your fix ends
Against the 50/30/20 budgeting rule
The 50/30/20 rule allocates 50% of net pay to needs (housing, bills, food, transport), 30% to wants, 20% to savings. Housing alone should not consume the whole needs bucket - standard UK guidance is below 28% comfortable, 28-35% stretched, above 35% risky.
Risky: Mortgage exceeds 35% of net income at the entered rate. Either increase the deposit, lower the price, or genuinely re-examine whether this purchase is sustainable.
Stress test: interest rate moves ±10pp
Your initial fixed-rate term ends in 2-5 years. After that, the variable rate you revert to could be materially higher or lower than today's quote.
| Rate | Monthly | % of net | Band |
|---|---|---|---|
| -10pp (0.00%) | £900 | 23.8% | Comfortable |
| -8pp (0.00%) | £900 | 23.8% | Comfortable |
| -6pp (0.00%) | £900 | 23.8% | Comfortable |
| -4pp (0.50%) | £958 | 25.3% | Comfortable |
| -2pp (2.50%) | £1,211 | 32.0% | Stretched |
| Entered (4.50%) | £1,501 | 39.7% | Risky |
| +2pp (6.50%) | £1,823 | 48.2% | Risky |
| +4pp (8.50%) | £2,174 | 57.5% | Risky |
| +6pp (10.50%) | £2,549 | 67.4% | Risky |
| +8pp (12.50%) | £2,944 | 77.9% | Risky |
| +10pp (14.50%) | £3,354 | 88.7% | Risky |
Bank of England base rate, last 100 years
UK mortgage rates have historically tracked the Bank Rate (with a few percentage points on top). The 1970s-80s peaks reached 17%; the 2009-2021 floor sat near zero. Source: Bank of England.
How often UK base rates have been at each level
Years out of the 101-year sample (1925-2025).
| Rate band | Years | % of time |
|---|---|---|
| Under 2% | 13 | 12.9% |
| 2-4% | 26 | 25.7% |
| 4-6% | 25 | 24.8% |
| 6-8% | 16 | 15.8% |
| 8-10% | 6 | 5.9% |
| 10-15% | 13 | 12.9% |
| 15% or higher | 2 | 2.0% |
Build a buffer before you stretch on price
- Your fixed-rate term ends in 2-5 years. The variable rate you revert to is set when the fix ends, not now.
- Over the last 100 years, UK base rates have been above 6% for 37% of the sample and above 10% for 15%. The 2009-2021 near-zero floor was an outlier, not the norm.
- Aim for a 3-6 month emergency fund before completion, plus a separate sinking fund that covers the £673/month difference between today's payment and a +4pp shock. Six months at that buffer is roughly £4,040 set aside.
- The cheapest place to absorb a rate rise is a lower house price today, not a bigger salary in two years.
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