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Loan Interest Calculator

Estimate the scheduled interest cost, regular payment, total repaid, and interest share for a fixed-rate loan.

Published

Total interest
Interest over the full term
$3,322.46
Regular payment
$111.02
Total repaid
$13,322.46
Principal borrowed
$10,000.00
Number of payments
120
Interest share of payments
24.94%

$10,000.00 at 6% for 10 years costs $3,322.46 in scheduled interest.

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Results update as you type.

Loan Interest Calculator

The loan interest calculator focuses on the cost of borrowing rather than the headline payment. It estimates scheduled interest for a fixed-rate amortizing loan, plus the regular payment, total repaid, principal borrowed, number of payments, and the percentage of all payments that goes to interest. If the first question is “What will I pay each month?”, start with the loan calculator. If the first question is “How expensive is the interest over the whole term?”, this page is the more direct tool.

The calculation is intentionally limited to scheduled principal and interest. It does not add origination fees, late charges, payment protection, insurance, taxes, or prepayment changes. It also assumes the rate stays fixed and every payment arrives on schedule. For comparing two offers side by side, the loan comparison calculator is a natural next step. For an existing debt where you want to know the remaining principal, the loan balance calculator addresses a different point in the loan life cycle.

What the result tells you

Interest over the full term is the primary result. It answers how many dollars the scheduled loan costs beyond principal if you follow the payment plan exactly. Regular payment is the installment calculated from the same inputs. Total repaid is all scheduled payments combined. Principal borrowed repeats the starting amount so the interest comparison is clear. Number of payments is the rounded count of years multiplied by the selected frequency. Interest share of payments shows what percentage of total repayment is interest rather than principal.

That last percentage can reveal the effect of time. A long loan may have a comfortable payment but a high interest share. A short loan may have a higher payment but much less total interest. The calculator makes that trade-off visible without mixing in unrelated costs.

Formula

The calculator first chooses the number of periods:

periods=round⁡(term years⋅payments per year)\text{periods} = \operatorname{round}(\text{term years} \cdot \text{payments per year})

It then converts the annual rate to a periodic rate:

periodic rate=annual rate100⋅payments per year\text{periodic rate} = \frac{\text{annual rate}}{100 \cdot \text{payments per year}}

For a positive rate, the regular payment is:

payment=principal⋅periodic rate1−(1+periodic rate)−periods\text{payment} = \frac{\text{principal} \cdot \text{periodic rate}}{1 - (1 + \text{periodic rate})^{-\text{periods}}}

The scheduled totals are:

total repaid=payment⋅periods\text{total repaid} = \text{payment} \cdot \text{periods}

interest=total repaid−principal\text{interest} = \text{total repaid} - \text{principal}

interest share=interesttotal repaid⋅100\text{interest share} = \frac{\text{interest}}{\text{total repaid}} \cdot 100

If the rate is 0%, the payment is principal divided by periods and the interest result is $0.

Worked example

For a $10,000 loan at a 6.0% annual interest rate over 10 years with monthly payments, the calculator uses 12 payments per year. The number of periods is 10 multiplied by 12, or 120. The periodic rate is 6.0 divided by 100 and divided by 12, which equals 0.005, or 0.5% per month.

The amortized payment formula gives a regular payment of $111.02. Multiplying $111.02 by 120 produces total repaid of $13,322.46. Subtracting the original $10,000 principal leaves $3,322.46 in scheduled interest. The interest share is $3,322.46 divided by $13,322.46, or 24.94% after rounding. Those values match the calculator output for the default inputs: total interest as the primary result, regular payment $111.02, total repaid $13,322.46, principal $10,000, 120 payments, and interest share 24.94%.

APR, interest rate, and the real borrowing cost

The annual rate entered here is treated as the periodic interest driver. APR is a broader comparison figure in many consumer credit disclosures because it can reflect certain finance charges. That distinction matters when fees are large. A loan with a lower note rate but high mandatory fees can have a higher APR than a cleaner loan with a slightly higher note rate. This calculator can estimate scheduled interest, but it cannot decide which disclosure number is best for a specific contract.

To approximate a financed fee, add it to principal. To evaluate an up-front fee, compare it separately with the interest savings from a lower rate. If two loans have different terms, compare total interest and total paid, not just the APR.

Ways to reduce interest

  • Borrow less if possible; interest is charged on the balance.
  • Choose a shorter term if the higher payment remains affordable.
  • Compare APRs and fees across several lenders before accepting an offer.
  • Make extra principal payments only after confirming there is no prepayment penalty and the lender applies the money to principal.
  • Track the payoff impact with the loan repayment calculator, then check budget fit with the budget calculator.

This material is informational and not financial advice. Your actual borrowing cost depends on the contract, fees, timing, credit approval, and lender servicing rules.

Sources

Frequently asked questions

What does total loan interest mean?
Total loan interest is the amount paid above the principal over the scheduled life of the loan. The calculator finds the regular amortizing payment, multiplies it by the number of payments, and subtracts the original amount borrowed to isolate that borrowing cost.
How is this different from a payment calculator?
A payment calculator centers on the installment you must budget for each period. This page centers on the interest cost created by that schedule, so the primary result is lifetime interest rather than the regular payment amount due each month.
Why does the form ask for payment frequency?
Payment frequency determines both the periodic rate and the number of scheduled payments. Monthly payments use 12 periods per year, biweekly uses 26, weekly uses 52, quarterly uses 4, and yearly uses 1. The interest estimate follows that selected rhythm.
Is the annual interest rate the same as APR?
Not always. The calculator applies the annual rate you enter directly to the balance. APR may include certain fees and disclosure adjustments, so lender APRs can be higher than the note rate that actually determines scheduled interest in the contract.

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