CostAccelerated biweekly payments are calculated as half your monthly payment, paid every two weeks — which works out to 26 half-payments (13 full payments) a year instead of 12. That one extra payment annually can shave several years off a 25-year amortization and save meaningful interest.
How the math actually works
An "accelerated" biweekly payment is set at exactly half of your monthly payment, but paid every two weeks rather than twice a month. Since a year has 52 weeks, that's 26 payments annually — the equivalent of 13 full monthly payments instead of the usual 12, all without you ever explicitly deciding to "pay extra." The 13th payment goes entirely to principal, since your regular payment already covers each period's interest.
A worked example
$450,000 loan, 5% rate, 25-year amortization
| Regular monthly payment | $2,622 |
| Accelerated biweekly payment | $1,311 × 26/yr |
| Years saved off amortization | ~3 years |
| Approximate interest saved | ~$28,000 |
See your own numbers, including the exact payoff date difference, on the extra & accelerated payment calculator.
Why it's not the same as "regular" biweekly
Some lenders also offer a "regular" (non-accelerated) biweekly option, which simply divides your monthly payment by exactly 2 rather than by half of the monthly amount you'd pay on an accelerated schedule — a subtle but real difference. Regular biweekly still totals exactly 12 months' worth of payments per year spread over 26 periods, with no extra payment and no additional principal reduction versus paying monthly. Accelerated biweekly is the version that actually saves you money; make sure you know which one your lender has you set up on, since the naming isn't always clearly explained.