Biweekly Mortgage Payments: The Extra Payment Hiding in the Schedule

Twenty-six halves are thirteen wholes

A year contains 52 weeks and a day, which is 26 fortnights. Pay half your monthly instalment on each of them and you pay 26 × $899.33 = $23,382.47 in the year. Twelve monthly instalments come to 12 × $1,798.65 = $21,583.82. The ratio is exactly 13 ÷ 12. You are not paying more often; you are paying more. The whole apparent magic of the fortnightly plan is one additional monthly payment a year, smuggled in by the mismatch between twelve months and twenty-six fortnights.

That is not an argument against doing it. The extra payment is genuinely powerful, because it lands entirely on principal and every unit of principal removed early stops accruing interest for the rest of the term. It is an argument against believing the frequency is what does the work — and, more practically, against paying anyone to arrange it. If the mechanism is one extra payment a year, you can produce the identical result by adding a twelfth of your instalment to each monthly transfer, at a cost of thirty seconds in your banking app.

Three schedules, actually run

The model is stated so it can be checked. Loan $300,000, nominal annual rate 6 percent. The monthly schedule accrues 0.5 percent a month and pays $1,798.65 for 360 months, from the standard annuity formula we derive in full elsewhere. The fortnightly schedule accrues 6 ÷ 26 percent every 14 days and pays $899.33 until the balance is gone. The third schedule accrues monthly, exactly like the first, and pays $1,798.65 plus one twelfth of it, $149.89, giving $1,948.54 a month.

The monthly schedule runs its full 360 payments and costs $347,515 of interest. The fortnightly one clears in 638 payments — 8,932 days, or 24 years and 5 months — for $273,079. The monthly-plus-a-twelfth one clears in 295 months, 24 years and 7 months, for $273,849. Put the two accelerated schedules side by side: they finish two months apart and $771 apart, on total interest of roughly a quarter of a million and a total saving of about $74,000. To the nearest tenth of a percent, they are the same plan.

Split the $74,436 total saving into its two causes and the proportions are stark: $73,666 of it — 99 percent — is produced by the thirteenth payment, which the monthly-plus-a-twelfth schedule also makes. The remaining $771, exactly 1 percent, is everything the fortnightly rhythm contributes on its own. And that residual is itself a mixture of small opposing effects rather than a mechanism: money arriving on average about a week earlier inside each month helps, twenty-six compounding periods a year instead of twelve very slightly hurts, and the fact that 26 fortnights is 364 days rather than 365 means a fortnightly plan drifts towards squeezing an extra payment into the calendar every fourteen years or so, which helps again. Its sign and size depend on the day-count convention in your contract. A number that can flip with a clerical convention is not the reason to choose a plan.

The fourth row of the table is the most instructive one. Make the extra payment as a single lump at the end of each year instead of spreading it, and the loan clears in 297 months for $276,591 — $3,513 worse than the fortnightly plan. That gap is 4.6 times the $771 that the fortnightly frequency itself is worth. In other words, when in the year you make the extra payment matters several times more than whether you pay every fortnight or every month. Spread it, and you have captured essentially all of the available benefit.

What the services sell, and what the lender actually does

Third-party plans exist that will set up fortnightly debits for you, typically charging an enrolment fee and sometimes a small charge per transfer. Price that against what the frequency is actually worth. Suppose an enrolment fee of $400 and a transfer charge of $2.50: over 638 debits the charges come to $1,595, plus the $400, which is $1,995 — 2.6 times the $771 the fortnightly rhythm contributes. The plan pays for itself only through the extra payment, which you can make for nothing. You are being sold a standing order.

There is a second, quieter problem. Many lenders do not accrue interest fortnightly at all. Their systems run on monthly cycles, so a fortnightly plan debits your account every two weeks, holds the money in a suspense account and releases one whole payment on each monthly due date; twice a year, when the held halves have accumulated into a spare whole payment, that surplus is applied to principal. This is often called an accelerated rather than a true fortnightly plan, and it produces our fourth schedule rather than our second: 297 months and $276,591, not 638 fortnights and $273,079. The residual advantage of the fortnight is not merely small in that arrangement, it is negative — your money sits idle in the lender's account between debit and application.

Only principal counts

An overpayment does nothing unless it reduces the balance on which interest is computed. Three common ways it fails to. It can be posted as an advance on next month's instalment, in which case the schedule is untouched and you have merely paid early. It can sit in a suspense account until it reaches the size of a whole payment. Or, on a loan where taxes and insurance are collected with the instalment, it can be swallowed by that escrow account instead of reaching the debt. Every one of these is a normal, documented behaviour rather than a scandal, and every one of them silently converts a $149.89 monthly overpayment into nothing at all.

The instruction that prevents all three is short: state in writing that the surplus is to be applied to principal, on receipt, without deferring the next scheduled instalment. Then verify it once, on the following statement, by checking that the balance fell by the amount of the instalment's principal portion plus the whole overpayment. If it did not, you have found the problem in month one rather than in year eight.

One more contractual check, and it is the one that differs most between countries. In the United States, prepayment penalties on owner-occupied loans have become rare, so overpaying is generally free. In continental Europe it is usually a contractual right with limits: German fixed-rate loans typically grant a Sondertilgungsrecht of around 5 percent of the original amount per year and charge a Vorfälligkeitsentschädigung beyond it, French contracts allow partial early repayment subject to a minimum amount and a capped indemnity, and Spanish and Portuguese contracts cap compensation by statute. None of that forbids the strategy in this article — one extra instalment a year is well inside every one of those allowances — but it does mean the contract, not the calculator, sets your ceiling.

The alternative: recasting, which does the opposite

Overpaying and recasting both start with money going to principal, and then diverge completely. Overpaying keeps the payment and shortens the term. Recasting keeps the term and lowers the payment: you pay a lump sum, the lender recomputes the instalment over the remaining months, and the maturity date does not move. It is not a refinance — the rate, the term and the contract are unchanged, and it usually costs a modest administrative fee rather than a full set of closing costs.

The trade is worth quantifying. Take the same loan five years in: after 60 payments the balance is $279,163 and $87,082 of interest has already been paid. Put $30,000 against it, taking the balance to $249,163, and you have two options. Keep paying $1,798.65 and the loan clears 237 months later — 297 months in total, 24 years and 9 months — with $263,365 of interest over its whole life. Recast instead, and the payment falls to $1,605.36, a relief of $193.29 a month, but the loan runs its full 300 remaining months and total lifetime interest reaches $319,527. The recast costs $56,162 more in interest than simply keeping the payment.

That does not make recasting wrong. It buys something an accelerated schedule cannot: a permanently lower required payment, which is exactly what a household with a fallen income, a new dependant or a variable-income year needs. Overpaying buys the opposite — a shorter loan at an unchanged monthly commitment. Choose by which constraint actually binds you. If cash flow is the binding constraint, recast; if it is total cost, keep the payment and let the term collapse.

What to do instead

Divide your instalment by twelve, add that to every monthly transfer, and instruct the lender in writing to apply the surplus to principal on receipt. On our loan that is $149.89 a month, and it captures $73,666 of the $74,436 that a fortnightly plan would deliver — 99 percent of the benefit, at no fee, with no third party in the chain and no money parked in anyone's suspense account. If your income genuinely arrives every fortnight and matching the mortgage to it makes the budget easier to hold, that is an excellent reason to pay fortnightly. Just understand that the reason is your cash flow, not the arithmetic, and check first that your lender applies the money the day it arrives.

Frequently asked questions

Is a fortnightly plan available on a European mortgage?

Rarely. Fortnightly and weekly mortgage payments are common in North America, Australia and New Zealand, where payroll cycles match them. In continental Europe the monthly direct debit is close to universal, and most lenders have no fortnightly product at all. What European contracts do offer instead is a contractual right to make partial early repayments — annual allowances, minimum amounts and, in some countries, statutory caps on any indemnity. The strategy in this article survives the difference intact, because it never depended on the fortnight: an extra instalment a year, paid as a twelfth added monthly or as a lump within your allowance, produces the same result under either system.

Is it better to make the extra payment early in the year or late?

Earlier is always better, and the size of the effect is measurable rather than theoretical. Spreading the thirteenth payment as a twelfth added each month costs $273,849 of interest; paying it as one lump each December costs $276,591. The $2,742 difference is nothing but timing within the year, and it is larger than the entire contribution of fortnightly frequency. If you can only make the payment as a lump, make it in January rather than December. If you can spread it, spread it.

How do I check that my overpayment reached the principal?

One arithmetic check on the next statement settles it. Note the closing balance before the payment, the interest charged for the month and the total you paid. The balance should fall by exactly the total paid minus the interest charged. On our loan in month one that is $1,948.54 minus $1,500.00, so a fall of $448.54 — the $298.65 of scheduled principal plus your $149.89 overpayment. If the balance fell by only $298.65, your surplus is sitting somewhere else: in a suspense account, in the escrow, or credited as an advance on next month. Call and have it reapplied, and put the standing instruction in writing so it does not recur.

Should I overpay the mortgage or invest the money instead?

Overpaying is a risk-free, tax-free return equal to your mortgage rate — 6 percent here — because every unit repaid stops costing 6 percent for the rest of the term. To beat it, an investment must earn more than 6 percent after tax with comparable certainty, which is a high bar. Two things cut the other way. Overpayment is illiquid: the money is in the walls, and getting it back means selling, refinancing or borrowing against the equity. And it does nothing for your required monthly payment, so it improves your net worth without improving your resilience. The conventional order still holds — clear expensive unsecured debt first, keep an emergency fund, take any matched pension contribution, and only then compare the mortgage rate with what the money would otherwise earn.

Does a recast change my interest rate or my contract?

No. That is precisely what distinguishes it from a refinance. A recast keeps the same lender, the same rate, the same maturity date and the same terms; it only recomputes the instalment over the remaining months on a smaller balance. There is no new underwriting, no valuation, no notary and no set of closing costs — usually just an administrative fee. A refinance replaces the loan entirely, which is what you want when the market rate has fallen enough to justify the costs, and what you do not want when the only thing you need is a smaller monthly payment on a rate you are happy with. Not every lender or loan type permits recasting, so ask before you send the lump sum, not after.