What your payoff result shows
The baseline is what the remaining interest costs if nothing changes. Everything else is measured against it, and each strategy is priced in the two currencies that matter: dollars of interest saved and payments removed.
Extra monthly payments and a biweekly schedule do the same thing by different routes — both put more principal in sooner. A lump sum is different in kind, because it has two possible uses, and the last two lines set them against each other.
Prepaying a lump sum keeps your payment the same and shortens the loan. Recasting the same money asks the lender to re-amortise the remaining balance over the remaining term, which lowers the payment and keeps the original end date. Identical money, opposite outcomes: one buys time, the other buys monthly cash flow. Almost no calculator shows both, and the decision is usually made without seeing either number.
How to use this calculator
- Balance remaining from your statement, not the original loan. Everything here works from where you are now.
- Your rate, which on an older mortgage may be far below or above today’s average — and that gap is what decides whether paying down early is even the right move.
- Years and months left. Your statement or amortisation schedule has the exact figure.
- Extra monthly, a lump sum, or both. Each is priced separately so you can see which does more for your situation.
- When the lump sum lands is in the advanced panel. Earlier is worth materially more, because the interest saved keeps compounding for the rest of the term.
Prepay or recast?
A recast is a re-amortisation. You pay a lump sum, the lender recalculates the payment over the remaining term, and your monthly obligation falls permanently. The rate does not change, there is no new underwriting, and the fee is usually a few hundred dollars rather than the thousands a refinance costs.
Prepaying the same lump sum without a recast leaves the payment untouched and simply removes months from the end of the loan. In pure interest terms prepaying wins, because the balance falls just as far but you keep paying the larger amount against it.
So the choice is not about which is cheaper — it is about what you need. Prepay if the goal is to be free of the mortgage sooner and the current payment is comfortable. Recast if the payment itself is the pressure: a lower obligation makes a household more resilient to a job change or a rate shock elsewhere, and that has a value the interest figure does not capture.
Two practical notes. Not all loans allow recasting — government-backed loans generally do not, and lenders usually require a minimum lump sum and a minimum number of payments made. And if the rate itself is the problem rather than the payment, a refinance is the tool, not a recast.
Does the biweekly trick actually work?
It works, and it is less magical than it sounds. Paying half your monthly amount every fortnight means 26 half-payments a year, which is 13 monthly payments rather than 12. The saving comes from that extra payment, plus the slightly earlier arrival of each half.
Two cautions. First, you can achieve nearly the same result by simply dividing one payment by twelve and adding it to each month — no arrangement with the lender required, and no third-party service needed. Firms charging a setup fee and a per-transaction charge to "manage" biweekly payments are selling you something you can do for free.
Second, check how your lender applies fortnightly money. Some hold each half payment until the full monthly amount arrives, in which case the timing benefit disappears and only the thirteenth payment remains. Ask before assuming.
Should you pay it off early at all?
This is the question the calculator cannot answer for you, and it turns on your rate. Paying down a mortgage is a guaranteed return equal to the interest rate — tax-free, risk-free and certain. That is genuinely attractive at 7% and much less so at 3%.
The comparison that matters is against everything else the money could do. In rough order of priority: capture any full employer retirement match, because nothing beats it; clear high-rate debt, which costs far more than any mortgage; build an emergency fund, since a paid-down mortgage is not spendable in a crisis; then weigh extra mortgage payments against investing the same money.
That last comparison is a genuine judgement call rather than a calculation. Expected investment returns are higher than most mortgage rates but uncertain; mortgage prepayment is lower but certain. The honest answer is that both are reasonable, that the certainty has real value, and that the illiquidity of home equity is the strongest argument for not overdoing it.
One trap to avoid: never prepay at the expense of your emergency fund. Money in a mortgage cannot be retrieved without borrowing it back, and a home equity line arranged in a crisis is arranged on the worst possible terms.
Where the money comes from matters
Extra payments have to come from somewhere, and the source changes whether the saving is real. Money redirected from spending is a straightforward win. Money redirected from retirement contributions usually is not, because you give up an employer match and decades of tax-sheltered growth to save interest at a single-digit rate.
Money borrowed to do it is worse again. Paying a mortgage down with a credit card advance or a personal loan swaps secured debt at a low rate for unsecured debt at a high one — the arithmetic is simply backwards, however satisfying the falling balance looks.
The one source that is almost always right is a windfall you were not counting on. A bonus, a tax refund or an inheritance applied to the balance lands entirely on principal and, unlike a monthly commitment, costs you no flexibility at all. That is why the lump-sum comparison above exists, and why the timing field is worth experimenting with: the same money applied five years earlier saves noticeably more.
One last check before committing anything. A mortgage prepayment is the least reversible thing you can do with cash — the money is gone into an asset you cannot spend, and getting it back means borrowing against the house. Make sure the emergency fund is genuinely funded first, because a plan that leaves you borrowing back at a worse rate has destroyed value rather than created it.
What this calculator assumes
- A fixed rate for the remaining term, and extra payments applied to principal on receipt.
- No prepayment penalty. Rare on US mortgages now, but worth confirming in your note.
- Principal and interest only. Escrow for tax and insurance continues either way and is unaffected — see the mortgage calculator for the full payment.
- The recast figure excludes the lender’s fee and assumes your loan permits one.
- Biweekly modelled at the fortnightly rate, which assumes the lender applies each half payment when it arrives rather than holding it.
- No tax effects. If you itemise and deduct mortgage interest, paying less interest slightly reduces that deduction — which lowers the effective benefit for a minority of filers.
These are planning estimates. Your servicer’s payoff quote is the authority, and extra payments should be labelled as principal-only when you send them.
Mortgage payoff questions people ask
How do I make sure extra money goes to principal?
Label it explicitly as a principal-only payment, using your servicer’s designated option rather than simply sending more. Unmarked extra money is sometimes applied to the next scheduled payment instead, which achieves almost nothing — check the statement afterwards to confirm the balance fell by the full amount.
Is it better to pay extra monthly or one lump sum a year?
Monthly wins slightly, because each dollar starts saving interest sooner. The difference is small, so the practical answer is whichever you will actually keep doing — a monthly transfer you automate beats an annual payment you intend to make.
Will paying extra lower my monthly payment?
No, not by itself. Prepayment shortens the loan while the payment stays the same. Lowering the payment requires a recast, which re-amortises the balance over the remaining term, or a refinance into a new loan.
Does paying off my mortgage early hurt my credit score?
Closing a long-standing instalment account can cause a small, temporary dip by reducing your credit mix and average account age. It is not a reason to keep a mortgage you can clear, and the effect fades.
Should I pay off the mortgage before retiring?
Many people prefer to, because it removes the largest fixed cost from a fixed income and reduces how much has to be withdrawn each year. Against that, using a large share of savings to do it reduces liquidity at exactly the age flexibility matters most — the retirement calculator is where to test both versions.