Bi-Weekly Mortgage Calculator Formula

Understand the math behind the bi-weekly mortgage calculator. Each variable explained with a worked example.

Use the Bi-Weekly Mortgage Calculator

Formulas Used

Bi-Weekly Payment

biweekly_pmt = biweekly_payment

Standard Monthly Payment

monthly_pmt = monthly_payment

Extra Principal Per Year

extra_per_year = extra_annual

Total Interest (monthly plan)

monthly_total_interest = monthly_payment * n - loan_amount

Equivalent Extra Monthly Payments/Year

equiv_extra_payments = 1

Variables

VariableDescriptionDefault
loan_amountLoan Amount(USD)300000
interest_rateInterest Rate(%)7
loan_term_yearsLoan Term(years)30
rDerived value= interest_rate / 100 / 12calculated
nDerived value= loan_term_years * 12calculated
monthly_paymentDerived value= r > 0 ? loan_amount * r * pow(1 + r, n) / (pow(1 + r, n) - 1) : loan_amount / ncalculated
biweekly_paymentDerived value= monthly_payment / 2calculated
annual_biweekly_totalDerived value= biweekly_payment * 26calculated
annual_monthly_totalDerived value= monthly_payment * 12calculated
extra_annualDerived value= annual_biweekly_total - annual_monthly_totalcalculated

How It Works

Bi-Weekly Mortgage Payments

Instead of making 12 monthly payments per year, you make 26 half-payments (every two weeks). This effectively adds one extra monthly payment per year.

Why It Works

  • 26 bi-weekly payments = 13 monthly equivalents per year
  • That extra payment goes directly to principal
  • Reduced principal means less interest charged on subsequent payments

    • Savings

  • Typically shaves 4-6 years off a 30-year mortgage
  • Saves tens of thousands in interest
  • Payment amount per paycheck is manageable since it is half the monthly amount

    • Implementation

    Some lenders offer formal bi-weekly programs (may have fees). Alternatively, you can achieve the same result by adding 1/12 of your monthly payment as extra principal each month.

    Worked Example

    A $300,000 loan at 7% for 30 years, comparing monthly to bi-weekly payments.

    loan_amount = 300000interest_rate = 7loan_term_years = 30
    1. 01Monthly payment: $1,995.91
    2. 02Bi-weekly payment: $1,995.91 / 2 = $997.96
    3. 03Annual cost (monthly): $1,995.91 x 12 = $23,950.92
    4. 04Annual cost (bi-weekly): $997.96 x 26 = $25,946.96
    5. 05Extra principal per year: $25,946.96 - $23,950.92 = $1,996.04 (one extra payment)
    6. 06Total interest (monthly): $1,995.91 x 360 - $300,000 = $418,527
    7. 07Bi-weekly plan saves approximately 5-6 years and $65,000+ in interest

    Frequently Asked Questions

    How much time does bi-weekly save on a 30-year mortgage?

    Bi-weekly payments on a 30-year mortgage typically reduce the loan term by 4 to 6 years, depending on the interest rate. At 7%, a 30-year loan is paid off in about 24-25 years. The higher the rate, the greater the time savings.

    Do I need my lender to set up bi-weekly payments?

    Not necessarily. You can self-manage by dividing your monthly payment by 12 and adding that amount as extra principal each month. This achieves the same annual result without potential lender program fees.

    Are there fees for bi-weekly payment programs?

    Some lenders or third-party services charge setup fees ($200-$400) and per-transaction fees ($2-$8 per payment). These fees reduce your savings. The self-managed approach of making one extra payment per year avoids all fees.

    Ready to run the numbers?

    Open Bi-Weekly Mortgage Calculator