Biweekly Mortgage Payment Calculator

Related Calculators

Table of contents

• How to use
• Common mistakes
• Definitions
• Methodology
• Limitations & assumptions
• Sources

Loan balance ($): The unpaid principal you still owe on the mortgage.

Principal: The part of a payment that lowers the loan balance.

Interest: The cost charged for borrowing money, based on the rate and the current balance.

Regular monthly payment: The estimated monthly principal and interest payment needed to pay off the loan over the time left. It is not your total housing payment if taxes, insurance, or escrow are included [1].

Payment every 2 weeks: Half of the regular monthly principal and interest payment, plus any extra amount you add.

Interest saved: The monthly-plan interest minus the selected biweekly-plan interest. A positive number means the biweekly plan costs less interest.

Time saved: The regular payoff time minus the selected biweekly payoff time, shown in months and usually explained as years and months.

How half-payments are handled: The rule for when your 2-week payment lowers the balance. This matters because interest depends on the balance used for each period.

Mistake: Using the original loan amount in Loan balance ($) .
Fix: Use the current unpaid principal balance from your statement.

Mistake: Typing your full housing payment into Regular monthly payment expectations, then thinking the calculator is too low.
Fix: Remember that Regular monthly payment is principal and interest only, not taxes, insurance, escrow, or HOA dues.

Mistake: Leaving Interest rate (percent per year) blank or entering a negative rate.
Fix: Enter 0 for a zero-interest loan, or enter the yearly rate as a non-negative percent such as 6 or 6.25.

Mistake: Entering the original 30-year term in Time left on loan (years) after you have already made payments for several years.
Fix: Enter the years left until payoff under the current monthly schedule.

Mistake: Adding your whole extra monthly amount to Extra added each 2-week payment ($) .
Fix: Enter only the extra amount you plan to add to each 2-week payment.

Mistake: Choosing How half-payments are handled as if every servicer credits half-payments right away.
Fix: Choose Held until a full payment if your servicer holds partial payments before applying them.

• The calculator estimates principal and interest only. It does not include property taxes, homeowners insurance, mortgage insurance, escrow changes, HOA dues, late fees, or prepayment fees.
• The true biweekly option assumes each 2-week payment is credited to the loan balance right away. Your servicer may use different timing.
• The held-until-full-payment option is a conservative estimate. It converts 26 half-payments per year into an even monthly amount and does not reproduce every servicer suspense-account rule.
• The rate is treated as fixed for the whole remaining term. Adjustable-rate loans can change after the rate resets.
• Results can differ slightly from a servicer payoff quote because lenders may use exact calendar days, payment posting dates, rounding rules, and required escrow handling.
• The final payment is allowed to be smaller than the usual payment so the estimate does not overpay the loan.

Monthly baseline

The calculator first estimates the regular monthly principal and interest payment. In an amortizing mortgage, each payment includes interest and principal, and the principal share generally grows as the balance falls [2].

months_left = Time left on loan (years) * 12

monthly_rate = Interest rate (percent per year) / 100 / 12

If monthly_rate > 0: Regular monthly payment = Loan balance ($) * monthly_rate * (1 + monthly_rate)^months_left / ((1 + monthly_rate)^months_left - 1)

If monthly_rate = 0: Regular monthly payment = Loan balance ($) / months_left

The monthly baseline is then simulated month by month. Each month, interest is added, the payment is applied, and the final payment is reduced if the regular payment would overpay the remaining balance.

interest_this_month = balance * monthly_rate

new_balance = balance + interest_this_month - payment

Biweekly plan

The biweekly payment is half of the regular monthly principal and interest payment plus any Extra added each 2-week payment ($).

Payment every 2 weeks = Regular monthly payment / 2 + Extra added each 2-week payment ($)

For Lower balance every 2 weeks, the calculator uses 26 two-week periods per year and applies each payment to the balance right away.

biweekly_rate = Interest rate (percent per year) / 100 / 26

interest_this_period = balance * biweekly_rate

new_balance = balance + interest_this_period - Payment every 2 weeks

For Held until a full payment, the calculator estimates the effect as an even monthly payment equal to 13 regular monthly payments per year, plus the yearly extra biweekly principal spread over 12 months.

held_monthly_payment = Regular monthly payment * 13 / 12 + Extra added each 2-week payment ($) * 26 / 12

Savings

Interest is the sum of interest charged during the payment loop. Payoff time is the first period where the payment can clear the remaining balance and that period's interest.

Interest saved = Interest with monthly payments - Interest with biweekly plan

Time saved = regular monthly payoff months - Biweekly payoff time

For example, a $300,000 balance at 6% with 30 years left has a regular monthly principal and interest payment of about $1,798.65. With a true biweekly plan and no extra added each 2-week payment, the payment every 2 weeks is about $899.33, the payoff time is about 294.46 months, and the interest saved is about $74,436.02.

Error checks

The calculator blocks a loan balance of $0 or less, a blank or negative interest rate, and a time left of 0 years or less. It treats a blank extra biweekly amount as $0, but invalid extra-payment text is an error. If a payment would not reduce the balance, the calculator stops and asks you to check the payment or rate.