Weekly Payment Amortization Calculator and Formula

A weekly payment amortization calculator estimates the level payment needed to repay a fixed-rate loan with weekly installments, along with the total paid and interest over the schedule. Enter the loan amount, annual APR, and term in years; the calculator below uses a 52-payment-per-year model and reports a weekly payment and estimated total interest.

Formula

For weekly installments, the calculator treats the annual percentage rate as a nominal annual rate divided into 52 equal weekly periods. It applies the standard level-payment amortization formula:

Weekly payment = round[P × r / (1 − (1 + r)⁻ⁿ), 2]

• P is the starting loan principal in dollars.
• APR is the annual percentage rate entered as a percentage, such as 8 for 8%.
• r is the weekly rate, calculated as APR ÷ 5,200. Dividing by 100 converts a percentage to a decimal, and dividing by 52 converts the annual rate to a weekly rate.
• n is the number of weekly payments, calculated as the loan term in years × 52.
• Weekly payment is rounded to the nearest cent before total interest is calculated.

The total-interest estimate is weekly payment × number of payments − principal. Since this calculator uses 52 weekly periods per year, the payment count is years × 52. The formula assumes equal payments and a constant rate throughout the term.

Worked Example

Using the calculator’s default inputs—$20,000 principal, 8% APR, and a five-year term:

1. Weekly rate: 8 ÷ 5,200 = 0.0015384615.
2. Payment count: 5 × 52 = 260 weekly payments.
3. Apply the payment formula: $20,000 × 0.0015384615 ÷ [1 − (1 + 0.0015384615)⁻²⁶⁰] = approximately $94.51 per week after rounding.
4. Total of rounded payments: $94.51 × 260 = $24,572.60.
5. Estimated total interest: $24,572.60 − $20,000 = $4,572.60.

The figures are estimates based on the stated assumptions; rounding each payment to cents can make the final payment differ slightly in an actual lender schedule.

Assumptions

• The interest rate stays fixed for the entire term.
• Payments are equal, made once per week, and assumed to occur at the end of each weekly period.
• Interest accrues using a weekly rate equal to APR divided by 52, with compounding at that weekly interval. This is a calculation convention; a lender may use a different day-count or accrual method.
• Fees, taxes, insurance, escrow, and other charges are not included.

How Weekly Amortization Works

Amortization means paying down a debt over time through scheduled installments. Each payment covers interest accrued since the prior payment and reduces principal. Early in a standard amortizing loan, the outstanding balance is larger, so more of each payment goes toward interest. As principal falls, the interest portion generally shrinks and more of each later payment reduces the balance.

A weekly schedule has more payment periods per year than a monthly schedule: 52 rather than 12. That does not automatically mean the loan has a lower total cost. The result depends on the rate convention, payment amount, timing, fees, and whether a quoted “weekly” amount is truly one installment each week or a different payment arrangement.

Use this estimate when you want to translate a principal, APR, and term into a regular weekly amount or understand the approximate interest implied by those inputs. It is also useful for comparing schedules on the same mathematical assumptions. It does not determine whether a payment fits a household budget or whether a lender will approve a loan.

Reading the Result and Comparing Payment Frequencies

The first result is the estimated amount of each weekly installment. Total interest is the sum of those rounded installments over the modeled term, less the original principal. Total payments can be found by adding principal and interest; in the default example, that is $24,572.60.

A monthly calculator cannot be compared fairly with a weekly calculator just by looking at the payment amount: one represents 12 payments a year, the other 52. To compare total cost, use the same principal, APR convention, term, fees, and payment timing, then compare total payments and the final payoff date. Even then, a lender’s actual schedule may differ because of its accrual and rounding rules.

Some arrangements collect a weekly amount equal to one-quarter of a monthly installment. That creates 52 quarter-payments, equivalent to 13 monthly installments per year, rather than simply dividing a standard annual total into 52 equal payments. This calculator does not model that arrangement; it recalculates a level payment over 52 periods per year.

Common Errors and Limits

• Entering APR as a decimal: Enter 8 for 8%, not 0.08. The calculator converts the percentage internally.
• Confusing weeks and months: The term is in years, and this model uses 52 payments per year. It does not use 4 weeks per month or 12 × 4 periods per year.
• Assuming every lender uses the same rate method: A quoted APR does not by itself establish the precise weekly accrual method, payment date, or fees used in a contract.
• Treating the final installment as exact: The displayed payment is rounded to cents. A real schedule may adjust its last payment to clear a small residual balance.
• Leaving out additional costs: The result excludes fees and other charges unless they are included in the principal or separately modeled.

The formula represents a fixed-rate, level-payment loan. It does not model variable rates, skipped or late payments, extra principal payments, balloon payments, changing payment dates, or lender-specific rounding. For the contractual payment and payoff schedule, use the figures and terms supplied by the lender.

Frequently Asked Questions

How do I calculate a weekly loan payment?
Convert APR to a weekly decimal rate by dividing the APR percentage by 5,200, calculate the number of payments as years × 52, then use the level-payment formula shown above. Round the payment to cents.

Is a weekly payment the same as a monthly payment divided by four?
No. There are 52 weeks in the model year and 12 months, so dividing a monthly installment by four produces 48 installments per year, not 52. Also, a lender’s weekly-payment product may use a different schedule or rate method.

Does paying weekly reduce total interest?
Not necessarily. The answer depends on the payment amount and timing, interest accrual, and loan terms. A weekly schedule can mean different things; compare the actual payment schedule and total repayment figures rather than assuming a saving.

Why does my lender’s weekly amount differ?
The lender may use different rounding, payment dates, day-count conventions, fees, or a different definition of weekly payment. Check the loan disclosure for the rate calculation and schedule details.

Can this calculator include extra weekly payments?
No. It estimates equal scheduled payments only. Extra payments change the balance and interest path, so they require a schedule that models when each extra amount is paid and how the lender applies it.

This result is an estimate, and the lender’s disclosure gives the exact figures.

Related

• Graduated Amortization Payment Calculator
• HELOC Payment Calculator With Amortization
• Free Amortization Schedule With Extra Payments

in p | Loan amount | $ | 20000 | 1 | 100000000
in apr | Interest rate (APR) | % | 8 | 0.01 | 100
in yrs | Loan term | years | 5 | 0.0833 | 50
out pmt | Weekly payment | $ | round(p * (apr / 5200) / (1 - (1 + apr / 5200) ^ -(yrs * 52)), 2) | 2
out int | Total interest | $ | pmt * yrs * 52 - p | 2