Loan Balance With Interest: Calculate What You Owe

This calculator estimates a fixed-rate loan’s monthly payment and total interest from the amount borrowed, APR, and term. Enter those figures to see the payment and interest over the full scheduled term; this is not the remaining balance after a particular number of payments.

Formula

For a fixed-rate loan repaid with equal monthly payments, the monthly payment is the amount needed to repay the principal and interest over the selected number of months:

PMT = P × r ÷ [1 − (1 + r)⁻ⁿ]

• P is the starting loan principal, in dollars.
• APR is the annual percentage rate, entered as a percent.
• r is the monthly interest rate as a decimal: APR ÷ 1200.
• n is the number of monthly payments: years × 12.
• PMT is the monthly payment, in dollars.

The calculator rounds the payment to cents. It estimates total interest as PMT × n − P, using that rounded payment. This follows the calculator’s stated level-payment model; an actual lender’s final scheduled payment may differ slightly because of rounding or its payment and interest rules.

Worked Example

Using the defaults—$20,000 principal, 8% APR, and a five-year term—calculate the monthly rate and number of payments:

1. Monthly rate: 8 ÷ 1200 = 0.0066667, or about 0.66667% per month.
2. Number of payments: 5 × 12 = 60.
3. Substitute in the payment formula: $20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰] ≈ $405.53 per month, rounded to cents.
4. Total scheduled payments using the rounded payment: $405.53 × 60 = $24,331.80.
5. Estimated total interest: $24,331.80 − $20,000 = $4,331.80.

The calculator’s headline result is a monthly payment of $405.53; its total-interest result is $4,331.80.

Assumptions

• The APR stays fixed for the entire term.
• There are equal monthly payments, made at the end of each monthly period.
• Interest is modelled monthly at APR ÷ 12, with no daily-interest adjustment.
• Fees, taxes, insurance, PMI, escrow, late charges, and extra payments are not included.

What You’ll Need

• The starting principal, not the original purchase price unless that is the amount financed.
• The loan’s APR as a percentage per year. Get the applicable figure from the lender’s disclosure; do not substitute a rate you have not confirmed.
• The repayment term in years. For a loan with a variable rate, changing payment, or unusual schedule, this calculator’s fixed-payment assumptions may not fit.
• A calculator is optional. The fields above perform the arithmetic, but you can use the formula to check the result.

Step-by-Step

1. Find the current balance or starting principal. To estimate a new loan’s scheduled payments, use the amount financed. To calculate what remains on a loan already in progress, use its current principal balance and the remaining term—not the original loan amount and original term.
2. Enter the APR. Use the annual percentage rate supplied for the loan, written as a percentage such as 8 for 8%. The calculator converts it to a monthly decimal by dividing by 1200. If the loan has a variable rate, any result assumes the entered rate remains unchanged.
3. Enter the applicable term. For a new loan, enter the full repayment term. For an existing loan, enter the remaining months converted to years where practical; the calculator treats the entered years as years × 12, so a precise month-based schedule may need a separate calculation.
4. Read the monthly payment. The first output is the estimated level payment needed to repay the loan over the entered term under the formula’s assumptions. It does not mean that amount is the exact amount due under every lender’s contract.
5. Read estimated total interest. The second output multiplies the rounded monthly payment by the number of months and subtracts principal. It represents interest across the whole entered term, not interest accrued so far.
6. For a balance after a known number of payments, use an amortization calculation. The formula is B_k = P(1+r)^k − PMT × [(1+r)^k−1] ÷ r, where B_k is the balance after k payments, and P, r, and PMT are defined above. This page’s calculator does not ask for k, so its outputs alone cannot give a dated remaining balance. For an exact current payoff or balance, check the lender’s statement or request a payoff figure.

Common Mistakes

• Confusing payment with balance. A monthly payment is what the formula schedules; it is not the outstanding principal. Early payments include interest, so the balance does not fall by the full payment amount.
• Using the wrong starting figure. A balance calculation for a loan already underway starts with the current principal and remaining schedule. Reusing the original principal can overstate the amount still owed.
• Entering APR in the wrong format. Enter 8 for 8%, not 0.08. The formula itself converts the percentage into a monthly rate.
• Mixing annual and monthly terms. This calculator asks for years and converts them to months. Do not enter the number of months in the years field.
• Rounding too soon. Keep full precision while calculating the rate and formula, then round the payment to cents. Small rounding differences can affect a total over many payments.
• Assuming every loan is level-payment. Interest-only periods, variable rates, irregular payments, fees added to principal, or extra payments change the schedule.

Tips

• Compare the result with the payment schedule in the loan disclosure. If they differ, check whether the amount financed, APR, term, or included charges differ.
• For a dated balance estimate, count payments that have actually posted and use the current principal and remaining payment terms. Payment timing matters because interest accrues between payments.
• Keep payment records and note any extra principal payments separately. An extra payment may reduce later interest, but its effect depends on how the servicer applies it.
• Use a lender-provided payoff figure when you need the amount to close the loan on a specific date. A displayed principal balance may not include interest accrued since the last payment or other contract charges.

Troubleshooting

The result looks too high or too low: Check whether the entered APR is a percentage, whether the principal is the amount actually financed, and whether the term is in years. Also confirm that you did not enter the original term when estimating an existing loan’s remaining payments.

Your lender’s payment differs: Review the disclosure for the exact principal, rate, payment frequency, term, and any amounts included in the payment. The lender may use a different schedule, payment date convention, or rounding method. Use its documented figures when reconciling an account.

You need the remaining balance, not a payment: This calculator does not include a payment-count field. Use the balance formula above with the number of posted payments and the applicable original schedule, or use the current principal shown by the lender. Do not treat total interest as the balance.

The loan has a changing rate or extra payments: A single fixed-rate calculation cannot reproduce a schedule that changes over time. Work period by period using the actual rate, payment, and transaction dates, or ask the lender for the current amortization schedule.

Frequently Asked Questions

How do I calculate a loan balance after several payments?
Use the balance-after-payments formula with the starting principal, monthly rate, scheduled payment, and number of payments made. Confirm that the payment amount and timing match the actual schedule.

Is total interest the same as the remaining balance?
No. Total interest is the estimated interest over the whole entered term. A remaining balance is the principal still unpaid at a particular point in the schedule.

Why does the first payment reduce principal by less than the payment?
Part of each payment covers interest accrued for that period. The remainder reduces principal; the split changes over time in a level-payment schedule.

Does APR always equal the interest rate used in this calculation?
Not necessarily. This simplified formula treats the entered APR as a fixed nominal annual rate divided into monthly periods. Contract terms and included costs can make an APR differ from the rate used to accrue periodic interest.

Does this include extra payments or fees?
No. It models equal monthly payments and excludes extra payments and fees. Those items can affect both the payoff date and amount of interest paid.

Can I use it for a variable-rate loan?
You can calculate an estimate for one assumed rate, but the result assumes that rate stays fixed for the full term. A rate change can alter the payment, balance, or repayment time.

This result is an estimate; 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 | $ | p * (apr / 1200) / (1 - (1 + apr / 1200) ^ -(yrs * 12)) | 2
out int | Total interest | $ | pmt * yrs * 12 - p | 2