Personal Loan Amortization Calculator and Payment Formula

A personal loan amortization calculator estimates your fixed monthly payment, total interest, and total of payments from the loan amount, APR, and term. Enter the figures from a lender’s disclosure to see how a level-payment loan is scheduled to repay; the estimate assumes the rate and payment stay unchanged.

Formula

For a fixed-rate loan repaid with equal monthly payments, the payment is calculated using the standard amortization formula:

Payment = round[P × r ÷ (1 − (1 + r)⁻ⁿ), 2]

• P is the amount borrowed, in dollars.
• r is the monthly interest rate, calculated as annual APR ÷ 1,200. For an 8% APR, r = 8 ÷ 1,200.
• n is the number of monthly payments, calculated as loan term in years × 12.
• Payment is the monthly amount, rounded to the nearest cent.

Total of payments is the rounded monthly payment multiplied by the number of payments. Total interest is that amount minus the original principal. Because the monthly payment is rounded to cents, the final scheduled payment may differ slightly in an actual lender schedule; this calculator uses the rounded payment for each month.

Worked Example

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

1. Convert the APR to a monthly rate: 8 ÷ 1,200 = 0.0066667, or about 0.66667% per month.
2. Find the number of payments: 5 × 12 = 60 months.
3. Apply the formula: $20,000 × 0.0066667 ÷ [1 − (1 + 0.0066667)⁻⁶⁰] = $405.53 when rounded to cents.
4. Total of payments: $405.53 × 60 = $24,331.80.
5. Total interest: $24,331.80 − $20,000 = $4,331.80.

The displayed results are therefore a $405.53 monthly payment, $4,331.80 in total interest, and $24,331.80 in total payments.

Assumptions

• The interest rate is fixed for the full term.
• Payments are equal, made monthly, and paid at the end of each monthly period.
• Interest is compounded monthly using APR divided by 12.
• Fees, taxes, insurance, and other charges are not included. If a lender finances a fee, use the resulting amount borrowed as the principal only if that matches the loan disclosure.

How Amortization Works

Amortization describes how each scheduled payment covers interest and reduces the amount owed. Interest for a period is based on the remaining balance, so the interest portion generally falls as the balance shrinks. With a fixed payment, the portion applied to principal generally rises over time. Early payments can therefore reduce the balance more slowly than a borrower expects, even though every payment is the same.

A schedule lists each period’s opening balance, interest, principal paid, and closing balance. In a simplified monthly schedule, interest is the opening balance multiplied by the monthly rate; principal paid is the payment minus that interest. The closing balance is the opening balance minus principal paid. The schedule repeats this calculation until the balance reaches zero, subject to any final-payment adjustment made by the lender.

When to Use the Calculator and How to Read It

Use the estimate to understand the arithmetic of a proposed fixed-payment personal loan or to compare loan structures using figures supplied to you. Keep the principal, APR, and term visible when reviewing results: a lower payment by itself does not mean a lower borrowing cost, since a longer term can spread repayment over more months and increase total interest.

• Monthly payment estimates the regularly scheduled amount under the stated assumptions.
• Total interest estimates the interest over all scheduled payments, not necessarily every charge connected with borrowing.
• Total of payments is the principal plus estimated interest in this model.

For example, the default calculation does not determine whether a lender will offer those terms. Enter the actual APR and amount from a disclosure, and check whether the stated APR or financed amount treats fees differently from the calculator’s assumptions. Rates, fees, and available amounts vary by offer; obtain the applicable figures from the lender rather than treating the example inputs as market information.

Common Mistakes and Limits

• Entering a percentage as a decimal: Type 8 for 8% APR, not 0.08. The calculator converts annual percent to a monthly decimal rate.
• Mixing months and years: The term field is in years, and the formula multiplies it by 12. Do not enter 60 for a five-year term.
• Assuming APR captures every payment: The formula uses APR as a periodic rate input but does not separately add fees or other charges. The lender’s disclosed payment may reflect details this simple model omits.
• Expecting an exact final balance: Rounding a payment to cents for every month can leave a small difference for the last payment. Lenders may calculate interest or adjust the last installment under their contract terms.
• Applying it to a changing-rate or irregular-payment loan: The formula assumes a constant rate and equal monthly installments. It does not model skipped payments, late charges, variable rates, or a different payment frequency.

Extra payments also change the schedule because they can reduce principal sooner, which can change future interest. This calculator does not include an extra-payment input, so its totals should not be interpreted as an accelerated-payoff estimate.

Frequently Asked Questions

What does a personal loan amortization calculator show?
It estimates the fixed monthly payment, total interest, and total scheduled payments from the principal, APR, and term. It is a mathematical estimate, not an approval or loan offer.

How do I calculate a personal loan payment?
Convert APR to a monthly decimal by dividing it by 1,200, convert the term to months, and use the fixed-payment formula shown above. Round the resulting payment to cents.

Why does a longer loan term usually change total interest?
The formula applies interest to the outstanding balance each month. Extending repayment means more monthly periods in which interest can accrue, even if the monthly payment is lower.

Does the calculator include fees?
No. It does not add origination charges, taxes, insurance, or other costs. Check the lender’s disclosure to understand which amounts are included in its quoted payment and APR.

Can I use this for extra payments or a variable-rate loan?
Not accurately. The calculation assumes equal monthly payments and an unchanged rate. Extra principal payments or a changing rate require a schedule that models those events.

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

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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
out tot | Total of payments | $ | pmt * yrs * 12 | 2