Personal Loan Interest Repayment Calculator

A personal loan interest repayment calculator estimates your monthly payment and total interest from the amount borrowed, annual percentage rate (APR), and repayment term. Enter those three figures to see the scheduled payment and the interest paid over the full term, assuming fixed-rate monthly payments.

Formula

The calculator uses the standard amortizing-loan payment formula, with monthly payments and a fixed rate:

• Monthly payment: M = P × r ÷ [1 − (1 + r)⁻ⁿ]
• Total interest: I = M × n − P
• Monthly rate: r = APR ÷ 1,200
• Number of payments: n = loan term in years × 12

Here, P is the principal borrowed 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 the total interest in dollars. For example, an APR of 8% becomes 0.08 ÷ 12, or 0.0066667, per month. The displayed payment is rounded to cents; total interest uses that rounded payment multiplied by the number of payments, less the original principal.

Worked Example

Using the calculator’s default values—$20,000 principal, 8% APR, and a five-year term—there are 5 × 12 = 60 monthly payments. The monthly rate is 8 ÷ 1,200 = 0.0066667.

Substitute into the payment formula:

M = 20,000 × 0.0066667 ÷ [1 − (1.0066667)⁻⁶⁰] ≈ $405.53 per month.

Then calculate interest using the rounded monthly payment:

I = $405.53 × 60 − $20,000 = $4,331.80 in total interest.

Assumptions

• The APR and payment amount stay fixed throughout the loan.
• Payments are made monthly at the end of each payment period.
• Interest accrues monthly using APR divided by 12; this is a simplified schedule calculation.
• Fees, taxes, insurance, and other charges are not included. The APR may reflect certain borrowing costs, but the calculator does not separately model fees or their timing.

When to Use the Calculator

Use the estimate to understand how the principal, rate, and term affect scheduled repayment. It can help you review a lender’s quoted payment, compare hypothetical loan scenarios using figures you supply, or see how a longer or shorter term changes interest under the same assumed APR. The calculation does not establish whether an application will be approved or whether a particular payment fits a personal budget.

For a meaningful estimate, use the amount you expect to borrow—not just the amount you plan to spend. If a lender deducts an origination fee from the proceeds, the cash received may be less than the loan principal you must repay. Ask the lender for the amount financed, net proceeds, APR, payment schedule, and any fees, then use the figures that match the question you are trying to answer.

How to Read the Results

Monthly payment is the modelled scheduled amount for each of the loan’s monthly installments. Total interest is the interest implied by those payments over the entire term; it is not the total amount repaid. In the example, total payments are $405.53 × 60 = $24,331.80. Of that sum, $20,000 repays principal and $4,331.80 is calculated interest.

Each payment on an amortizing loan covers interest accrued for the period and reduces principal by the remaining amount. Early in the schedule, a larger share of a payment generally goes toward interest because the outstanding balance is higher. As principal falls, the interest portion falls and more of each level payment goes toward principal. The calculator summarizes the full schedule rather than showing each month’s allocation.

Common Mistakes and Limits

• Entering APR as a decimal: enter 8 for 8%, not 0.08. The calculator converts the percentage to a monthly decimal rate.
• Mixing annual and monthly terms: the term field is in years, and the formula multiplies it by 12. Do not enter the number of months there.
• Treating an estimate as a quote: lender calculations may use exact dates, daily interest, payment rounding, fees, or other contract terms that this simplified formula does not represent.
• Assuming total interest includes every cost: it does not. Separate fees and charges can make the total amount paid higher.
• Ignoring rate type: the result assumes a fixed APR. A variable rate can change, so its future payment and interest cannot be represented by one fixed-rate calculation.

The payment formula requires a positive interest rate, so the calculator’s APR input begins above zero. At a true 0% rate, payment would simply be principal divided by the number of payments, but that is outside this calculator’s stated input range. Values are rounded for display, so a lender’s final installment may differ slightly if it adjusts the schedule to account for rounding.

Frequently Asked Questions

How do I calculate interest on a personal loan?
For a fixed-rate loan with level monthly payments, calculate the monthly payment from the principal, monthly rate, and number of payments. Multiply that payment by the payment count and subtract the principal to estimate total interest.

Does the calculator show total repayment?
It shows monthly payment and total interest. Add the principal to total interest to get the modelled total repayment. In the example, $20,000 + $4,331.80 = $24,331.80.

Is APR the same as the interest rate?
They are related but are not always identical. APR is an annualized borrowing-cost figure and may account for certain fees under the lender’s calculation. Use the rate and cost figures provided in the loan disclosure, and ask the lender how its APR is calculated.

Why does a longer loan term usually mean more total interest?
With the same principal and fixed rate, extending the repayment period means the balance takes longer to pay down and more payment periods accrue interest. The monthly payment may be lower, while total interest may be higher.

Does this estimate include extra payments?
No. It assumes the scheduled level payment only. Extra principal payments can change the balance and interest schedule, and their effect depends on when they are made and how the lender applies them.

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

Related

• Personal Loan Calculator With Origination Fee: Payment, Cash and APR
• 50/30/20 Budget Calculator
• Debt-to-Income Ratio Calculator (DTI)

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