Amortization Schedule Creator: Calculate Loan Payments

An amortization schedule creator calculates a fixed monthly loan payment and shows how each payment is divided between interest and principal over time. Enter the loan amount, annual interest rate, and term to see the estimated payment and total interest; this calculator gives summary figures rather than a month-by-month table.

Formula

The calculator first finds a level monthly payment using the standard fixed-rate loan payment formula, then subtracts the original principal from the sum of those payments to estimate total interest.

• Monthly payment: M = round[P × r ÷ (1 − (1 + r)⁻ⁿ), 2]
• Total interest: I = M × n − P
• Monthly rate: r = APR ÷ 1200
• Number of payments: n = years × 12

Here, P is the loan principal in dollars, APR is the annual percentage rate entered as a percentage, r is the monthly rate as a decimal, n is the number of monthly payments, M is the monthly payment in dollars, and I is estimated total interest in dollars. The payment is rounded to cents before the total-interest calculation. Actual loan schedules may differ when the lender uses different payment dates, rounding, or other terms.

Worked Example

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

1. Convert the APR to a monthly decimal rate: r = 8 ÷ 1200 = 0.0066667.
2. Convert the term to monthly payments: n = 5 × 12 = 60.
3. Substitute into the payment formula: M = $20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰].
4. The payment is approximately $405.53 per month after rounding to cents.
5. Total interest = $405.53 × 60 − $20,000 = $4,331.80.

These results describe the same fixed-payment estimate: 60 payments of $405.53 total $24,331.80, of which $4,331.80 is interest under the formula.

Assumptions

• The interest rate stays fixed for the full term.
• Payments are made monthly, on schedule, with the first payment one month after the loan begins.
• Interest accrues monthly using APR divided by 12.
• The calculation excludes fees, taxes, insurance, PMI, escrow, late charges, and any extra or missed payments.

What an Amortization Schedule Shows

A full amortization schedule lists each payment period separately. For every month, it commonly shows the opening balance, payment, interest charged, principal repaid, and closing balance. At the start of a typical level-payment loan, the balance is high, so more of the payment goes toward interest. As principal falls, the interest portion generally declines and the principal portion rises. The scheduled payment remains level when the rate and loan terms remain unchanged.

For example, interest for a period is often calculated from the outstanding balance and the period’s rate. The portion left after that interest is applied reduces principal. The next period’s interest is then based on the lower balance. This pattern is why paying the same amount every month does not mean the same amount of principal is repaid each month.

This page calculates the payment and total interest, not every row of that schedule. To create a detailed table, each period needs to be calculated in sequence, accounting for the prior period’s ending balance and the lender’s exact rounding and payment-date conventions.

When to Use the Estimate

Use the calculator to understand the basic payment mechanics or to check how the entered loan amount, APR, and term relate mathematically. It can help you inspect a stated loan scenario, but it cannot establish whether a loan is suitable, affordable, or available. Enter the rate and terms supplied for the particular loan; do not treat the example defaults as a quote.

A longer term generally spreads repayment across more installments. With a positive fixed rate, this commonly lowers the scheduled monthly payment while increasing the number of periods over which interest accrues. A shorter term usually means fewer payments, but the monthly amount from the formula may be higher. The exact results depend on the inputs and the loan’s contractual details.

Common Errors and Limits

• Entering a decimal instead of a percent: Enter 8 for 8% APR, not 0.08. The calculator converts the percentage to a monthly decimal internally.
• Confusing APR with a monthly rate: APR is entered annually. Do not divide it by 12 before entering it.
• Assuming total interest includes every borrowing cost: This formula models interest on principal only. Fees and other charges can change the amount paid.
• Expecting the last payment to match exactly: Real schedules can have small differences from payment rounding, dates, and lender-specific calculations.
• Applying it to changing balances or rates: The formula assumes one fixed principal at the start, a fixed rate, and equal scheduled payments. It does not model variable-rate changes, interest-only periods, balloon payments, or extra payments.

The total-interest figure uses the rounded monthly payment multiplied by the number of payments, as specified here. A lender’s schedule may instead adjust the final payment or calculate interest using daily balances, so its exact total may not match this estimate.

Frequently Asked Questions

What does an amortization schedule creator do?
It estimates a loan’s regular payment and can show how each installment is allocated between interest and principal. This calculator returns the payment and estimated total interest, not a complete month-by-month table.

How do I calculate a monthly loan payment?
Convert the annual APR to a monthly rate by dividing it by 1,200, convert the term to months, then apply the fixed-payment formula shown above. The result is rounded to cents in this calculator.

Why does the interest portion decrease over time?
For a fixed-rate amortizing loan, interest is calculated against the remaining balance. As payments reduce that balance, less interest is due in later periods, leaving more of a level payment to reduce principal.

Does total interest include loan fees or insurance?
No. This calculation estimates interest from the principal, APR, and term only. It does not include fees, taxes, insurance, escrow, or other charges.

Can I use this for a variable-rate loan?
Not for a reliable full-term estimate. The formula assumes the APR stays fixed. A changing rate can alter both the payment and the interest schedule, so use the applicable loan terms and disclosures for the actual figures.

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

Related

• Interest Rate Table Calculator and Loan Payment Formula
• Interest Rate to APY Calculator: Convert and Compare
• Interest Rate Swaps: How They Work and What They Cost

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 | Monthly payment | $ | round(p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -(yrs * 12)), 2) | 2
out int | Total interest | $ | pmt * yrs * 12 - p | 2