Interest Calculator — Calculate Loan Payment or Simple Interest in Seconds

Loan tool below; scroll for simple interest—both fast and free

Use this free interest calculator to estimate loan payments or simple interest on any amount. No signup required.

Last updated: March 2026

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Monthly Payment

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Total Interest

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Total Payment

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Year-by-year split: interest breakdown. Walk-through: payment example. Simple vs compound · Loan · Car · Mortgage

Simple interest calculator

I = P × R × T — principal, annual rate as a decimal, time in years.

No monthly payment schedule? Use this block. For installments, use the loan section above.

Simple Interest (I)

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Total Amount (P + I)

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Estimates only. Home · Mortgage · Car loan

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How interest and loan payments work

When you borrow money, you pay interest (the cost of borrowing) plus principal. This page offers two tools: a loan calculator for monthly payments (car, personal, mortgage) and a simple interest tool for lump-sum scenarios. Compare with our main loan calculator, car loan calculator, simple interest calculator, mortgage calculator, or personal loan calculator.

How to use this calculator

This page has two tools:

  1. Loan section (top) — Enter loan amount, annual rate, and term in months to get monthly payment, total repayment, and total interest. Use this for car loans, personal loans, mortgages, and other installment debt.
  2. Simple interest block — Enter principal, annual rate, and time in years to get total interest and total amount. Use this when there’s no monthly payment schedule (e.g. a single lump-sum loan).

Real-world example

For a $20,000 loan at 8% over 48 months, the loan tool shows a monthly payment of about $488, total repayment of $23,410, and $3,410 in interest. The same $20,000 at 8% for 4 years as simple interest would be $6,400 in interest (I = 20,000 × 0.08 × 4)—different because the loan tool models amortization, where you pay principal down over time.

What affects your loan interest

What to know when you use this tool

Simple interest grows only on the original principal (I = P × R × T). Amortizing loans charge interest on the declining balance each month. Planning figures only—contracts may use different rules or fees. For business term debt, try our business loan calculator; for vehicles, the car loan calculator; for mortgages, the mortgage calculator; for simple vs compound side-by-side, the simple interest calculator or main loan calculator.

Frequently asked questions

What is the simple interest formula?
I = P × R × T, where P is principal, R is the annual rate as a decimal (5% → 0.05), and T is time in years. Total repayment is P + I if nothing else changes.
Why is loan interest usually higher than simple interest?
With amortization you pay interest on the outstanding balance while you gradually pay principal down. Simple interest ignores that schedule and only multiplies the starting principal by rate and time.
Does the simple section compound?
No. Simple interest does not compound on itself. Compound growth needs a different formula (see our simple interest page for a side-by-side example).
Can I enter a rate as monthly?
This page expects an annual rate for both tools. If you only have a monthly rate, convert carefully or confirm with your lender before relying on the output.
Does this include loan fees?
No. Fees would need to be added to principal manually if they are financed, or tracked outside the calculator.
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