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

    Ready to run the numbers?

    Open Bi-Weekly Mortgage Calculator