How Biweekly Mortgage Payments Work
The biweekly mortgage strategy is one of the simplest ways to pay off a home loan faster without refinancing or dramatically changing your budget. Instead of making one payment per month (12 per year), you make a payment every two weeks (26 per year). Since 26 half-payments equals 13 full monthly payments, you effectively make one extra full payment every year without it feeling like a large lump sum.
That extra payment goes directly to reducing your principal balance, which means less interest accrues over the remaining term. Because mortgage interest is calculated on the outstanding balance, every dollar you pay down early saves you interest in every subsequent period.
The Formula
The standard monthly mortgage payment uses the amortisation formula:
Monthly payment = P × [r(1+r)n] / [(1+r)n - 1]
Where P is the loan principal, r is the monthly interest rate (annual rate / 12), and n is the number of monthly payments (years × 12).
The biweekly payment is calculated as half the standard monthly payment. Over a year, you make 26 such payments (26 × half-payment = 13 full monthly equivalents). To model the payoff period, the remaining balance after each biweekly payment is recalculated using the biweekly interest rate (annual rate / 26).
Worked Example
Using the default inputs: a $600,000 loan at 6.5% per annum over 30 years.
| Detail | Monthly Schedule | Biweekly Schedule |
|---|
| Payment amount | $3,792.41 per month | $1,896.20 every 2 weeks |
| Payments per year | 12 | 26 (= 13 monthly equiv.) |
| Loan term | 30 years | approximately 24.2 years (24 yrs 2 mths) |
| Total interest paid | approximately $765,267 | approximately $589,023 |
| Interest saved | - | approximately $176,244 |
| Years saved | - | approximately 5.8 years |
The exact figures from the calculator above match these defaults. Results will vary with different loan amounts, rates, or terms.
Biweekly vs Fortnightly in New Zealand
New Zealand lenders commonly offer fortnightly repayment, which works identically to biweekly: 26 payments per year. When setting up fortnightly payments with your bank, confirm that the payment amount is set to exactly half your monthly repayment amount. Some banks may default to dividing the annual repayment by 26, which produces a slightly different payment and a smaller interest saving. The half-monthly method is the standard biweekly approach and produces the larger saving shown in this calculator.
Other Ways to Pay Down Your Mortgage Faster
- One extra payment per year: If your lender does not offer biweekly payments, making one additional voluntary payment equal to your monthly amount achieves roughly the same result.
- Round up your payments: Rounding up to the nearest $100 or $500 reduces the principal slightly faster each period.
- Lump sum payments: Putting tax refunds, bonuses, or inheritance funds directly onto your mortgage can have a significant impact because of the compounding interest effect.
- Shorten your loan term: Refinancing to a shorter term (for example, from 30 to 20 years) forces faster paydown but raises the monthly commitment.
Related Calculators
Sources and method: Standard mortgage amortisation formula (principal, interest, term). Biweekly savings modelled by iterating a balance reduction schedule at the biweekly rate (annual rate / 26) with 26 half-monthly payments per year. Consistent with methods described by the Consumer Financial Protection Bureau (CFPB) and ANZ, ASB, BNZ, Westpac NZ mortgage documentation.
This calculator provides indicative estimates only. Actual savings depend on your lender's exact calculation method, whether they apply payments immediately or at month-end, break fees, and any applicable loan conditions. Consult your lender or a registered financial adviser before making changes to your mortgage structure.
