Personal Loan Calculator: Payment With Interest

A personal loan calculator with interest estimates your fixed monthly payment and total interest from the loan amount, APR and repayment term. Enter those three figures to see the payment first, followed by the estimated interest paid over the full term.

Formula

The calculator uses the standard amortizing-loan payment formula. It converts the annual percentage rate (APR) to a monthly rate, then calculates a level monthly payment that pays interest and gradually repays the principal over the selected number of months:

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

• P is the amount borrowed, in dollars.
• APR is the annual percentage rate entered as a percentage per year.
• r is the monthly rate, calculated as APR ÷ 1,200. For example, an 8% APR gives a monthly rate of 0.0066667.
• n is the number of monthly payments, calculated as loan term in years × 12.
• round(…, 2) rounds the regular payment to the nearest cent.

Total interest is calculated as monthly payment × number of payments − principal. Because the payment is rounded to cents before this calculation, the displayed interest uses the rounded payment. A lender’s final schedule can differ slightly because of payment dates, daily interest calculations, fees or other contract details.

Worked Example

Using the calculator’s default inputs—$20,000 borrowed, 8% APR and a 5-year term—the calculation is:

1. Convert the APR to a monthly rate: 8 ÷ 1,200 = 0.0066667.
2. Convert the term to payments: 5 × 12 = 60 monthly payments.
3. Apply the payment formula: $20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰] = $405.53 after rounding to cents.
4. Calculate total interest using that rounded payment: $405.53 × 60 − $20,000 = $4,331.80.

Under these assumptions, the estimated monthly payment is $405.53, and estimated total interest is $4,331.80. The sum of the rounded payments is $24,331.80, including repayment of the $20,000 principal.

Assumptions

• The interest rate is fixed for the entire repayment term.
• Payments are equal, made monthly, and treated as occurring at the end of each monthly period.
• Interest is modelled monthly using APR ÷ 12; actual lender calculations may use different conventions.
• The estimate excludes fees, taxes, insurance, optional products and any other charges not entered as inputs.

How to Use and Read the Estimate

Use the amount you expect to borrow, the APR quoted for that loan and the planned repayment term. Enter APR as a percentage, such as 8 for 8%, not 0.08. Enter the term in years. The first result is the level monthly payment; the second is the estimated interest over all scheduled payments.

The monthly payment includes both interest and principal. Early in an amortizing loan, more of each payment generally goes toward interest; as the outstanding balance declines, a larger share goes toward principal. This does not mean the interest rate itself rises or falls. The total-interest figure is the sum of the interest implied by the model across the full schedule.

For a useful estimate, use the APR and term from the lender’s written loan offer rather than relying on a general rate assumption. If the offer includes an origination charge or other amount deducted from the proceeds, distinguish the amount financed from the cash you receive: the calculator models only the principal entered. Ask the lender which figures apply to the payment schedule and compare the written payment disclosure with this estimate.

What Changes the Payment and Interest?

• Loan amount: Holding the rate and term constant, borrowing more increases the payment and total interest.
• APR: A higher entered rate increases the amount of interest accrued and generally raises the monthly payment.
• Term: Spreading repayment over more months generally lowers the scheduled monthly payment but gives interest more time to accrue. The total interest can therefore be higher.
• Extra payments: Additional principal payments can change the payoff date and interest, but this calculator assumes only the regular fixed payment. It does not model a prepayment schedule or contract terms.

These are mathematical effects within the model, not a recommendation about borrowing or choosing a term. A payment estimate alone does not show all costs or determine whether a lender will offer particular terms.

Common Calculation Mistakes and Limits

A frequent error is entering the APR as a decimal. Since the calculator divides the percentage by 1,200, enter 8 for 8% rather than 0.08. Another error is confusing the monthly payment with total repayment: multiply the rounded monthly amount by the number of payments to estimate all scheduled payments, then subtract principal to isolate interest.

The formula assumes one fixed APR and equal monthly payments. It does not calculate a variable-rate loan, irregular payment dates, late charges, payment holidays, optional add-ons, or a changing balance caused by extra payments. It also does not determine whether an advertised APR includes a particular fee or whether the amount entered is the principal actually financed. Use the loan documents for those details.

Rounding matters over a long schedule. The calculator rounds the monthly payment to cents and uses that rounded amount to estimate total interest, as shown in the example. A lender may adjust the final payment by a small amount to bring the balance to zero, so the estimate and final schedule need not match exactly.

Frequently Asked Questions

How do I calculate a personal loan payment with interest?
Convert APR to a monthly rate by dividing the percentage by 1,200, convert years to months, and apply the amortizing payment formula shown above. The calculator performs those steps and rounds the payment to cents.

Does the monthly payment include interest?
Yes. Each scheduled payment includes interest for that period and a portion that repays principal. The split changes over time even when the total payment stays level.

How much interest will I pay on a personal loan?
For this fixed-payment estimate, multiply the rounded monthly payment by the number of payments and subtract the original principal. The result depends on the amount, APR, term and the lender’s calculation method.

Why is my lender’s payment different from the calculator?
Possible reasons include a different financed amount, fees included in the loan, a different APR, payment timing, daily-interest calculations or rounding. Check the figures and assumptions against the lender’s disclosure.

Does a longer loan term reduce total interest?
Not usually within this fixed-rate amortization model. A longer term generally lowers the scheduled payment but allows interest to accrue over more months, which can increase total interest.

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

Related

• Debt-to-Income Ratio Calculator (DTI)
• Credit Card Payoff Calculator: Months to Pay Off and Interest
• Personal Loan Calculator With Origination Fee: Payment, Cash and APR

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