Early Mortgage Payoff Calculator

What the choice involves

Paying a mortgage down faster than the schedule requires trades one thing for another: interest that will never be charged, against money that is no longer available for anything else. The arithmetic on the first half is exact and this calculator does it: years cut from the term and interest removed over the life of the loan, from a repeating monthly overpayment. The arithmetic on the second half depends on what the money would otherwise have done, which varies by household and by jurisdiction and is outside the model. The sections below describe how the comparison is usually set up, without settling it.

Reading the result rows

The headline is years cut from the term, rounded to one decimal, so it sits within a fraction of a month of the underlying month count; the Months Saved row carries that count, and it is the row to read when a difference of weeks matters. New Term is the accelerated payoff on the same one-decimal rounding. Interest Avoided has no scale on its own, so the row beneath it reports the interest the original schedule would have charged, and the row after that states the first as a share of the second. Total Extra Paid is the cash actually committed over the accelerated term, accumulated from the schedule rather than counted as the extra times the number of months, since the final month rarely takes a full instalment, and where the extra is small relative to the contractual payment it usually carries none of the extra at all. A much larger rounding sits on the input side rather than the output: the remaining term is entered in whole years, so a part-year has to be rounded to the nearest one, which can move the baseline by up to six months.

Total Extra Paid can come out larger than Interest Avoided, which looks like a loss and is not one. The extra is principal paid sooner, not money spent on top: both schedules repay the same principal, so the only difference in total cash leaving the household is the interest, and it falls by exactly the figure the Interest Avoided row reports. At the sample figures used on this page the original schedule pays out 350,754.02 over its life and the accelerated one 308,911.43, a gap of 41,842.59 against the 41,842.60 that row states, and the penny between them is the two totals rounding independently, not a difference in the underlying figures. What the extra buys is not a smaller total outlay than the extra itself; it is a smaller total outlay than carrying on unchanged, delivered sooner.

The core math

An overpayment removes interest at the mortgage rate, on the balance it reduces, for as long as that balance would otherwise have run. That last clause is the part most often left out. How much interest a unit removes depends on the rate and on the remaining term together, and the term can dominate: a unit applied to a low-rate balance with decades left can remove more interest than the same unit applied to a high-rate balance with a few years left. Comparing a mortgage against any other use of the money therefore means comparing two rates and two horizons, not two rates.

The alternatives differ in more than rate. Easy-access savings pay a headline rate that may be taxed, so the net figure is what compares. Cash inside a tax-advantaged account, where one is available, is closer to a like-for-like comparison. Broad equity investing carries an expected return rather than a known one, with volatility and sequence-of-returns risk attached, and expectations for it differ by source and by period. An employer match on retirement contributions, where offered and unused, is a return on the contribution before any investment return is counted. Contributions that reduce taxable income carry an uplift that depends on the jurisdiction and the marginal rate. Consumer debt at a high rate removes interest quickly but usually over a short remaining term, which is the rate-and-horizon point above. None of these is ranked here: the arithmetic differs by household, and the figures that would settle it are not inputs to this calculator.

Overpayments early against late in the loan

The same overpayment removes far more interest early in a loan than late, and the reason is not the composition of the payment. It is that principal removed in a given month is removed from the interest calculation of every month that follows, so an overpayment made when many months remain works across all of them. At the sample figures used on this page (a 200,000 balance at 5% over 25 years), a single 10,000 overpayment removes about 22,900 of interest at the outset, 15,900 after five years, 10,400 after ten, 6,000 after fifteen and 2,600 after twenty. The decline tracks the remaining term rather than the payment's interest share.

Overpayment caps and prepayment fees

Many mortgage contracts cap penalty-free overpayments, commonly at a percentage of the outstanding balance each year, with a fee (an early-repayment charge in some markets, a prepayment penalty in others) applying above the cap. The wording matters more than it looks: a cap set against the outstanding balance shrinks every year as the balance falls, so it is not a fixed annual allowance. A 25-year term overpaid to a 10%-of-balance cap from the outset clears in roughly nine to eleven years across a 2% to 8% rate, recomputing the allowance at each anniversary. Reading the same cap as a fixed amount fixed at the first year's balance gives six to seven years, but that reading breaches the cap from the second year onward, because the balance it was calculated on no longer exists. The loan agreement is where the cap and the fee are defined, and neither is modelled here.

The overpayment against investing comparison

For a household with a fixed monthly amount available for either, the comparison is between a known return at the mortgage rate and an expected return carrying risk. Two things make it easy to get wrong. The first is the basis: a mortgage rate is nominal, and an investment return quoted in real terms has already had inflation taken out of it, so the two cannot be compared until both are on the same footing: a real return has to be grossed up by expected inflation, or the mortgage rate deflated by it, before the gap means anything. The second is the horizon: the investment side compounds over whatever period the comparison runs, while the overpayment side stops removing interest once the mortgage is gone.

Beyond the arithmetic, the two differ in what they demand of the household. Money routed to overpayment is committed by the payment instruction; money routed to investing has to be invested each month and left there through whatever the market does. Where those two are not equally likely to happen, the comparison of expected returns is not the comparison being made.

How tax treatment changes the comparison

Several account types receive treatment that changes the after-tax return without changing the underlying investment. An employer match on retirement contributions adds to the contributed amount directly. Contributions that reduce taxable income carry an uplift set by the marginal rate. Accounts where growth or withdrawals are sheltered raise the after-tax return over long horizons relative to a taxable equivalent. Each of these changes the number on one side of the comparison, and by how much depends on the jurisdiction, the account type and the household's own position, which is why this page describes the mechanisms rather than putting them in an order.

The near-retirement recalculation

Several things change as a mortgage runs into retirement. The investment horizon shortens, which narrows the expected-return premium over the known return an overpayment provides. Sequence-of-returns risk rises, because mortgage payments met by selling assets during a downturn near retirement lock in the fall. And a household's income profile usually changes at retirement, so a payment that was comfortable against employment income may not be against a pension. Some households describe a mortgage-free retirement as simpler to manage than a mortgaged one at the same level of wealth, and weigh that alongside the arithmetic.

The final years

Once a balance is small relative to what it started at, most of each payment is principal and the remaining interest tail is small in cash terms. Clearing the balance outright ends the monthly commitment; the interest it removes is modest, because there was not much left to remove. Continuing to amortise keeps the capital available for something else, and the edge there is small but real where the alternative return exceeds the rate. At that point the difference between the two is rarely large enough to turn on the arithmetic, and households often decide on how simple they want their finances to be.

Offset and redraw variants

Whether these features exist at all depends on the market and the lender, and availability has changed over time, and the loan documentation is the source of truth. Where an offset feature is offered, cash held in a linked account reduces the balance that interest is calculated on without paying down principal, so the linked cash effectively earns the mortgage rate while staying accessible. A redraw facility works the other way round, allowing overpaid amounts to be withdrawn again. Both change the liquidity position that a plain overpayment gives up, which is one of the differences the comparison above turns on.

Common overpayment patterns

Households that overpay tend to do it in a few recognisable ways: an automated recurring transfer alongside the contractual payment, so the overpayment happens without a monthly decision; irregular cash such as a tax refund or a bonus directed at the balance instead of spending; overpayment beginning once a cash reserve is already in place, so the money committed to the property is not money that might be needed back; and annual overpayments tracked against whatever cap the contract states. This calculator models only the first of those: a fixed amount, every month, from the first month.

What this calculator does not model

The model holds the rate fixed for the whole term, applies the extra payment every month from the first, and assumes the contractual payment itself is unchanged, with no recast to a lower payment, no payment holiday, no rate reset at the end of a fixed period. It does not model a one-off lump sum, overpayment caps or the fees charged above them, arrangement or exit fees, tax treatment of any kind, or any alternative use of the money. What it produces is the difference between two fixed schedules at one rate.