Planner
Work backwards from what you can spare
Tell us what's realistic each month and we'll rank the ways to use it — then solve for the date you want to be free.
£300
Ranked · what £300 a month can do
Step up the monthly payment 10% a year
No lump sums — the monthly payment itself grows
Saved
£78.8 K
Time
13y 4m
Extra paid
£142.9 K
Monthly top-up
with every monthly payment
Saved
£50.8 K
Time
6y 11m
Extra paid
£64.8 K
Quarterly top-up
every three months
Saved
£50.4 K
Time
6y 11m
Extra paid
£64.8 K
Yearly lump sum
saved up, paid once a year
Saved
£48.7 K
Time
6y 10m
Extra paid
£64.8 K
Ranked by interest saved for the same outlay. Paying earlier always beats paying later — that's where the interest lives.
To hit 2045
About £231 extra a month.
The smallest monthly amount, rounded up to the next whole unit, that clears it by 2045. Found by running your full schedule repeatedly and narrowing in — the same maths as the table, not a shortcut.
Work backwards
Build your plan on the left. Watch it pay off on the right.
No Calculate button — every number updates as you type, and each figure traces back to a row in your schedule.
- 1
Your loan
What you owe today
- 2
Your overpayments
Lump sums or top-ups
- 3
Choose the outcome
Shorter loan or lower monthly payment
- 4
Results, live
No Calculate button
Your loan
What you owe today
Computed from the numbers above.
Your overpayment plan
1 active · £47.4 K overpaid over the loan
from 05 Nov 26
On its own: saves £37.6 K and 5y 1m off your loan.
What should overpaying do?
The single most important choice here
Advanced optionsPayment frequency, rate changes, fees — optional
Payment mechanics
Interest rate changes
Your monthly payment is recomputed over the term remaining, so the end date does not move. Your lender's letter says which it does.
Fees & charges
Only if your deal has one — see your mortgage offer for the rate and allowance.
Of the balance at the start of each calendar year — check your offer.
Net benefit after fees
£37.6 K
No fees entered, so the whole saving is yours.
Where you stand after
Side by side
Your loan with your plan, and without it
Two futures for the same loan. The right-hand column is the one you're building.
Interest you keep
£37.6 K
23% less interest than doing nothing
Time you get back
5y 1m
earlier than Sep 2051
Every figure here is the last row of the matching schedule below — nothing is estimated separately.
Visual proof
Your balance reaches zero 5y 1m sooner
The shaded gap is what you no longer owe. At its widest it is £75.7 K.
Where each year's instalments go
Interest outweighs principal until 2034 — which is why an overpayment made before then removes the most.
What waiting costs you
What £30.0 K removes from your interest bill, by the date you pay it.
Paid now it removes £51.4 K. Wait twelve months and it removes £48.2 K — £3.2 K less for the same money.
Full detail
Every payment, to the penny
239 payments across 21 years, every penny accounted for
21 years match
| # | Date | Opening | Payment | Interest | Principal | Overpayment | Closing |
|---|---|---|---|---|---|---|---|
| £250,000 | £4,548 | £2,775 | £1,772 | £400 | £248,228 | ||
| £248,228 | £18,990 | £10,882 | £8,108 | £2,400 | £240,120 | ||
| £240,120 | £18,990 | £10,514 | £8,476 | £2,400 | £231,644 | ||
| £231,644 | £18,990 | £10,129 | £8,861 | £2,400 | £222,783 | ||
| £222,783 | £18,990 | £9,726 | £9,264 | £2,400 | £213,519 | ||
| £213,519 | £18,990 | £9,306 | £9,684 | £2,400 | £203,835 | ||
| £203,835 | £18,990 | £8,866 | £10,124 | £2,400 | £193,711 | ||
| £193,711 | £18,990 | £8,406 | £10,584 | £2,400 | £183,127 | ||
| £183,127 | £18,990 | £7,925 | £11,065 | £2,400 | £172,062 | ||
| £172,062 | £18,990 | £7,423 | £11,567 | £2,400 | £160,495 | ||
| £160,495 | £18,990 | £6,897 | £12,093 | £2,400 | £148,402 | ||
| £148,402 | £18,990 | £6,348 | £12,642 | £2,400 | £135,760 | ||
| £135,760 | £18,990 | £5,774 | £13,216 | £2,400 | £122,544 | ||
| £122,544 | £18,990 | £5,174 | £13,816 | £2,400 | £108,728 | ||
| £108,728 | £18,990 | £4,546 | £14,444 | £2,400 | £94,284 | ||
| £94,284 | £18,990 | £3,890 | £15,100 | £2,400 | £79,184 | ||
| £79,184 | £18,990 | £3,204 | £15,786 | £2,400 | £63,398 | ||
| £63,398 | £18,990 | £2,487 | £16,503 | £2,400 | £46,896 | ||
| £46,896 | £18,990 | £1,738 | £17,252 | £2,400 | £29,643 | ||
| £29,643 | £18,990 | £954 | £18,036 | £2,400 | £11,608 | ||
| £11,608 | £11,791 | £183 | £11,608 | £1,400 | £0 | ||
How we calculate
No black box. You can check every number here.
Questions people ask
What if my target date is not achievable?
The planner will say so rather than returning a misleading figure. If clearing the balance by your target would require an overpayment beyond a plausible range, it reports the goal as unreachable. Move the target later, or use the ranking to see what the money you do have available actually buys.
Does this account for my early repayment charge?
Only if you enter it. Under Advanced options, add the charge, your penalty-free allowance and the date your deal ends. The charge is then applied only to each calendar year's overpayments above the allowance, and only until the deal ends — which is how lenders apply it — and subtracted from the net benefit. Most fixed and discounted deals allow around 10% a year without charge, so a modest monthly overpayment often attracts none.
Is it better to overpay monthly or save up for a yearly lump sum?
Monthly, if the only question is interest. Each overpayment starts reducing the balance from the next payment, so money paid in through the year works for longer than the same money held back and paid at the year end. The planner's ranking prices the gap on your own mortgage. It does not count interest the money might earn in savings while you wait, so set that against the gap yourself.
Why you can check this one
This site is not a lender, a broker or an affiliate of either, and nothing on it is ranked by what it pays us — because nothing does. Who makes this, and how it is paid for.
Nothing you type is sent anywhere. No account, no tracking of your loan details, nothing stored on a server. How that works.
Read the full methodology — the exact rate conversion, where rounding is applied, how we time an overpayment, and every choice we make differently from a lender, with the reasoning for each.
In plain terms
Planning backwards from a date instead of forwards from a payment
Most calculators ask what you will pay. This one also answers the more useful question: what would it take?
Working forwards — "if I overpay £200 a month, when am I clear?" — is the easy direction, and every calculator does it. Working backwards is the direction people actually think in: "I want to be mortgage-free by the time the children start university; what does that cost me each month?" There is no closed-form answer to that question, because the payoff date is not an invertible function of the overpayment. It has to be solved numerically.
The planner does exactly that. It runs your complete schedule repeatedly, adjusting the monthly overpayment and narrowing the interval until the payoff date lands on your target. It is the same engine and the same arithmetic as the schedule table below — not a simplified approximation used only for this panel — so the figure it returns will reconcile exactly with the schedule when you apply it.
It also answers the question in the other direction, which is often the more honest one. Tell it what you can genuinely spare each month and it ranks the ways to deploy that money: as a monthly overpayment, quarterly, saved up and paid annually as a lump sum, or as a steadily rising payment. Paying earlier beats paying later in every ranking it produces, because that is where the interest lives.
- Solved, not estimated
- The target figure comes from running your full schedule repeatedly and narrowing in, so it reconciles exactly with the table below.
- Rounded up
- The monthly figure is rounded up to the next whole pound. Rounded down it would fall short of the date it is quoted against.
- Ranked by
- Interest saved for the same outlay — not by how early each option starts, though that is usually the reason one wins.
- Still check
- Your annual overpayment allowance and any early repayment charge. A plan the arithmetic likes can still cost you at the deal stage.
How it's calculated
The working behind the number
This mortgage payoff calculator works backwards. Give it the year you want to be mortgage-free and it finds the monthly overpayment that clears the balance by then, by re-running your full schedule and narrowing the amount until the payoff date lands on target. Give it what you can spare each month instead and it ranks the ways of paying that money in by the interest each one saves.
- Written byThe CutYears team
- Last reviewed11 September 2026
- Sources2 primary, dated
The formula
Balanceₖ = Balanceₖ₋₁ × (1 + r) − Monthly payment − X, solved for the smallest X that brings the balance to 0 by your target date
- Balanceₖ₋₁
- What you owe before payment k. The first is the outstanding balance you enter.
- r
- The monthly rate: your annual rate ÷ 12.
- Monthly payment
- Your contractual repayment, from P × r × (1 + r)ⁿ ÷ ((1 + r)ⁿ − 1), or the figure you type.
- X
- The monthly overpayment the planner solves for.
Assumptions and limits
- The overpayment is the same every month from your next payment, and your monthly payment stays the same, so the term shortens.
- The amount is found by re-running the full schedule repeatedly and narrowing in, so it reconciles with the schedule table.
- Interest is charged monthly on the reducing balance at the annual rate ÷ 12, rounded to the penny each month; lenders that charge interest daily will differ slightly.
- An early repayment charge does not change the overpayment needed — it is paid out of pocket, never added to the balance — but is subtracted from the net benefit if you enter it.
A worked example
Take £250,000 outstanding at 4.45% a year, with 25 years (300 monthly payments) of term left, and a goal of being clear by the end of 2045.
- Monthly rate r = 4.45% ÷ 12 = 0.3708%.
- As it stands the term runs to Sep 2051.
- The planner searches the full schedule for the smallest monthly overpayment that clears it by the target.
£231 a month on top of the monthly payment clears it in Dec 2045, saving £42.1 K of interest.
| Opening balance | £250,000 |
|---|---|
| Annual rate | 4.45% |
| Term remaining | 300 months |
| Monthly payment | £1,383 |
| Total interest, no overpayment | £164,748 |
| Cleared | Sep 2051 |
Computed by the calculator on this page, from the figures it opens with.
Sources
- FCA Handbook, MCOB 12.3: an early repayment charge must be a reasonable pre-estimate of the lender's costs — checked 10 September 2026
- Bank of England, Effective interest rates, July 2026: 4.45% effective rate on new UK mortgages — the rate this page opens on — checked 10 September 2026