The Calculation Behind Bi-Weekly Mortgage Payments
The calculator uses a standard amortization formula. First, it computes the monthly payment:
monthly payment = loan x (r / (1 - (1 + r)^-n))
Where r = annual rate / 12 and n = years x 12. The bi-weekly payment is simply half the monthly payment. Because you make 26 bi-weekly payments per year (every 2 weeks), you pay the equivalent of 13 monthly payments annually instead of 12. That extra payment goes directly to principal, reducing the balance faster and cutting total interest.
For a $300,000 loan at 6.5% over 30 years: monthly payment = $1,896.20, bi-weekly payment = $948.10, total interest with monthly payments = $382,633.47, total interest with bi-weekly = $295,377.18, saving $87,256.29.
Example: $300,000 Mortgage at 7% for 30 Years
| Metric | Monthly Schedule | Bi-Weekly Schedule |
|---|---|---|
| Payment | $1,995.91/month | $997.95 every 2 weeks |
| Total Interest | $418,526.69 | $316,102.23 |
| Interest Saved | -- | $102,424.46 |
| Loan Payoff | 30 years | 23 yrs 9 mo |
| Time Saved | -- | 6 yrs 3 mo |
At 7%, bi-weekly payments save over $102,000 and eliminate more than 6 years of payments. The higher the interest rate, the more dramatic the savings: at 7.5%, the same $300,000 loan saves $119,231.45 and finishes 6 years 8 months early.
How Loan Size Affects Bi-Weekly Savings
The bi-weekly advantage scales linearly with loan amount. Here is a comparison at 6.5% over 30 years:
| Loan Amount | Bi-Weekly Payment | Interest Saved | Time Saved |
|---|---|---|---|
| $200,000 | $632.07 | $58,170.86 | 5 yrs 10 mo |
| $300,000 | $948.10 | $87,256.29 | 5 yrs 10 mo |
| $400,000 | $1,264.14 | $116,341.72 | 5 yrs 10 mo |
Time saved remains constant at the same rate and term, but dollar savings increase proportionally. A $400,000 borrower saves nearly $30,000 more than a $300,000 borrower.