Quarterly Amortization Schedule Calculator

A quarterly amortization schedule calculator estimates the payment due each quarter and shows how each payment is divided between interest and principal until the loan is repaid. Enter the loan amount, annual interest rate, and term in years; the results below use equal quarterly payments and a fixed rate.

Formula

The calculator uses the standard fixed-payment amortization formula, adapted to four payment periods per year. First, it finds the quarterly rate by dividing the annual percentage rate by 400. It then calculates a level payment that repays the starting principal and interest over the total number of quarters:

Payment = P × r / [1 − (1 + r)⁻ⁿ]

• P is the original loan principal, in dollars.
• r is the quarterly interest rate as a decimal: APR (%) ÷ 400.
• n is the number of quarterly payments: term in years × 4.
• Payment is the amount due each quarter, in dollars.

The displayed payment is rounded to cents. Total interest is calculated as the rounded quarterly payment multiplied by the number of payments, minus the original principal. This makes the estimate consistent with the displayed payment, although actual lender schedules can differ because of their rounding and payment-allocation procedures.

Worked Example

Using the calculator’s default inputs—$20,000 principal, 8% annual rate, and a five-year term—the loan has 20 quarterly payments. The periodic rate is 8% ÷ 400 = 0.02, or 2% per quarter.

1. Substitute into the payment formula: $20,000 × 0.02 ÷ [1 − (1.02)⁻²⁰].
2. Calculate the result: the quarterly payment is approximately $1,223.82 after rounding to cents.
3. Calculate total paid using the displayed payment: $1,223.82 × 20 = $24,476.40.
4. Subtract the principal: $24,476.40 − $20,000 = $4,476.40 in estimated total interest.

These are estimates from the formula and default assumptions. Small differences from a lender’s schedule can arise if it calculates interest using exact calendar days or rounds each period differently.

Assumptions

• The interest rate is fixed throughout the loan term.
• Payments are equal, made at the end of each quarter, with the first payment one quarter after borrowing.
• Interest compounds quarterly at APR ÷ 4, consistent with the calculator’s quarterly-period model.
• Fees, taxes, insurance, PMI, escrow, late charges, and extra payments are not included.

How a Quarterly Schedule Works

An amortization schedule is a period-by-period record of the payment, interest charge, principal repaid, and remaining balance. At the start of each quarter, interest is calculated on the outstanding balance. The payment covers that interest first; whatever remains reduces principal. Because the balance generally falls over time, the interest portion usually shrinks and the principal portion grows, while the scheduled payment stays level.

For a schedule row, a simplified calculation is:

• Quarterly interest = balance before payment × quarterly rate.
• Principal repaid = payment − quarterly interest.
• New balance = balance before payment − principal repaid.

For example, on a $20,000 starting balance at 2% per quarter, the first quarter’s interest is $400. With a $1,223.82 payment, approximately $823.82 goes to principal, leaving about $19,176.18. The next quarter’s interest is calculated on that lower balance. A full lender schedule may show slightly different cents due to its exact conventions.

When to Use It and How to Read the Result

Use quarterly periods when the contract calls for payments every three months, or to make a general estimate for a loan with quarterly installments. It can help you understand the payment size implied by a principal, rate, and term, and estimate total interest under the stated assumptions.

The quarterly payment is not a monthly payment or an annual payment. A quarterly schedule has four installments per year, so the total paid over a year is approximately four times the displayed installment. Do not divide the quarterly payment by three and treat that as a lender’s monthly bill: the timing of payments changes how interest accumulates and principal declines.

For a more detailed schedule, repeat the period calculations for each quarter, using the previous period’s ending balance as the next period’s starting balance. The last payment may need adjustment to clear a small residual balance created by rounding. This calculator reports the level payment and total interest, not every individual row or a final adjusted payoff amount.

Common Mistakes and Limits

• Entering the wrong rate format: enter an annual percentage such as 8 for 8%, not 0.08. The formula converts the percentage to a quarterly rate.
• Confusing APR with a periodic rate: the input is an annual rate; the calculation divides it by four. If a contract defines interest using a different method, this estimate may not match.
• Using the wrong payment frequency: a quarterly term means four payments per year. The formula is not appropriate unchanged for monthly, biweekly, or irregular installments.
• Assuming every loan has level payments: variable rates, interest-only periods, balloon payments, deferred payments, and irregular schedules are not represented.
• Overlooking rounding: the formula rounds the scheduled payment to cents and uses that rounded amount for total interest. A servicer may calculate and round interest on each due date, producing a small difference.

The estimate does not establish the amount legally due or include charges outside principal and interest. Check the loan documents or lender’s payment disclosure for the actual payment amount, schedule, and calculation method.

Frequently Asked Questions

How do I calculate a quarterly loan payment?
Convert the annual rate to a quarterly decimal by dividing the percentage rate by 400, multiply the term in years by four to get the number of payments, then use the fixed-payment formula shown above.

How many quarterly payments are in a five-year loan?
There are 20 scheduled quarterly payments in five years: five years × four quarters per year. Actual due dates can depend on the contract and calendar.

Is quarterly interest the same as annual interest divided by four?
This calculator assumes it is: the quarterly periodic rate is APR ÷ 4. A loan that accrues interest using daily balances, a different compounding convention, or another contractual method may produce different figures.

Why does the interest portion decline over time?
With a level payment and a falling balance, each quarter’s interest charge is lower. More of the unchanged payment can therefore go toward principal as repayment progresses.

Does this calculator include fees or extra payments?
No. It estimates principal-and-interest payments for a fixed-rate loan with regular quarterly installments. Fees and extra payments require separate inputs and can change the schedule.

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

Related

• Amortization Schedule by Date: Calculate Each Payment
• Amortization Schedule Builder: Payments and Balance
• Biweekly Amortization Schedule Calculator

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 | Quarterly payment | $ | p * (apr / 400) / (1 - (1 + apr / 400) ^ -(yrs * 4)) | 2
out int | Total interest | $ | pmt * yrs * 4 - p | 2