Mortgage Overpayment & Payoff Calculator
See exactly how much interest and how many years you shave off your mortgage with monthly or lump-sum overpayments — and check against your annual Early Repayment Charge (ERC) cap.
- 100% client-side mortgage math — your loan balance and financial scenarios never leave your browser.
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Mortgage details
Current balance, rate and remaining term
Overpayment plan
Standard payment is £1,493/mo
Data as of Nov 2026 · Source: your lender's mortgage terms. The 10% penalty-free cap and ERC schedule vary by lender and product — the defaults here are typical UK fixed-rate terms, not advice; check your offer letter
How this is calculated
With monthly rate r = (annual_rate / 100) / 12 and n = years × 12 + months, the baseline contractual payment is M = P · [r(1 + r)^n] / [(1 + r)^n − 1].
Each month t = 1..n, interest is charged on the opening balance I_t = B_(t-1) · r, and your total principal reduction is min(B_(t-1), M − I_t + extra_monthly + lump_sum_t). Because every extra unit of principal immediately reduces next month's interest base, savings compound over the remaining term.
UK and Australian fixed-rate mortgages commonly allow overpaying up to 10% of the opening annual balance per mortgage year without triggering an Early Repayment Charge (ERC).
Result
Payoff in 16 yrs 4 mo instead of 22 yrs
ERC lock-in penalty & offset account module
Fix expires 1 Nov 2029 (36 mos / 3 yrs left)
| Repayment strategy | Gross interest saved | ERC penalty deducted | Interim net savings interest | Net benefit | Payoff term |
|---|---|---|---|---|---|
| Path A · Pay immediately (absorb ERC) | £69,904 | −£260 | £0 | £69,644 | 13 yrs 10 mo |
| Path B · Cap at 10%/yr & clear excess after 1 Nov 2029 | £69,264 | £0 | +£396 | £69,660 | 13 yrs 11 mo |
Included in Pro. Unlock once, keep it on this device.
Month-by-month balance trajectory
Baseline schedule (dashed) vs accelerated payoff (solid)
| Year | Baseline bal. | Accelerated bal. | Overpaid | ERC status |
|---|---|---|---|---|
| Year 1 | £243,189 | £235,126 | £8,000 | OK (32% of cap) |
| Year 2 | £236,065 | £224,570 | £3,000 | OK (13% of cap) |
| Year 3 | £228,614 | £208,528 | £8,000 | OK (36% of cap) |
| Year 4 | £220,821 | £196,749 | £3,000 | OK (14% of cap) |
| Year 5 | £212,669 | £184,429 | £3,000 | OK (15% of cap) |
| Year 6 | £204,144 | £171,543 | £3,000 | OK (16% of cap) |
| Year 7 | £195,226 | £158,065 | £3,000 | OK (17% of cap) |
| Year 8 | £185,899 | £143,968 | £3,000 | OK (19% of cap) |
| Year 9 | £176,143 | £129,224 | £3,000 | OK (21% of cap) |
| Year 10 | £165,939 | £113,801 | £3,000 | OK (23% of cap) |
| Year 11 | £155,266 | £97,671 | £3,000 | OK (26% of cap) |
| Year 12 | £144,103 | £80,799 | £3,000 | OK (31% of cap) |
| Year 13 | £132,428 | £63,153 | £3,000 | OK (37% of cap) |
| Year 14 | £120,216 | £44,696 | £3,000 | OK (48% of cap) |
| Year 15 | £107,442 | £25,390 | £3,000 | OK (67% of cap) |
| Year 16 | £94,082 | £5,198 | £3,000 | Over cap (+£461) |
| Year 17 | £80,109 | £0 | £750 | Over cap (+£230) |
| Year 18 | £65,493 | £0 | £0 | — |
| Year 19 | £50,206 | £0 | £0 | — |
| Year 20 | £34,216 | £0 | £0 | — |
| Year 21 | £17,492 | £0 | £0 | — |
| Year 22 | £0 | £0 | £0 | — |
| Lifetime interest | £144,275 | £99,983 | £58,750 | Saved £44,292 |
What people hate about the other tools
We read the reviews of the incumbents before writing this page. Every complaint below maps to a decision in the tool above.
Just chuck it all in the offset — standard overpayment calculators only model direct principal paydown and ignore offset liquidity and tax rules.
In this toolCompares direct principal overpayment, offset account balance, and after-tax savings side by side.Fixed-rate mortgages usually cap penalty-free overpayments at 10% per year, but standard calculators never track the cap or deduct ERC penalties.
In this toolMonitors the 10% annual penalty-free allowance in real time and deducts ERC fees from net interest saved.Most online calculators only shorten the mortgage term and lack a toggle to keep the same term while lowering future monthly payments.
In this toolProvides a one-click toggle and side-by-side view comparing Term Reduction against Payment Reduction.
One-line difference: All-in-one UK/AU/US calculator modeling multi-lump-sum timelines, 10% ERC penalty caps, offset accounts, and LTV drops.
Free forever, Pro when you need the paperwork
Free no signup, no card
- Monthly & single lump-sum interest savings and payoff date forecast
- Side-by-side Term Reduction vs. Payment Reduction mode comparison
- Basic 10% annual penalty-free overpayment cap alert for fixed rates
Pro $12 once
- Irregular multi-lump-sum timeline & LTV remortgage tier simulator
- Tiered Early Repayment Charge (ERC) net savings deduction engine
- Offset account vs. after-tax savings comparison & PDF/CSV export
Pricing benchmarked against what the incumbents charge. See the full monetization map → · Already paid? Restore access
The tool runs locally in your browser — nothing you type is uploaded. The ad slot on this page is served by Google. See all 27 tools · Privacy · How these are paid for