Interest Calculator—Amortizing Loan + Simple I = P×R×T

Start with the loan tool below; scroll for simple interest—both free

Monthly Payment

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Total Payment

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Total Interest

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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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Two ways interest adds up

Simple interest only grows on the original principal. I = P × R × T—nothing “rolls up” unless the principal changes.

Amortizing loans (most cars, homes, personal loans) charge interest on the balance each month. Payments stay flat, but early payments are mostly interest.

Total interest on an installment loan is often higher than simple interest on the same numbers—you don’t pay all principal on day one.

Which tool should you use?

Simple block: principal + annual rate + years → total interest (no payment schedule).

Loan section: term in months → payment, total paid, total interest.

Compare simple vs compound on our simple interest calculator. Quick payments only: loan calculator.

Reading results responsibly

Planning figures only. Contracts may use different day-count rules, rounding, or fees.

Match annual vs monthly rates to your lender’s quote. Business term debt: business 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.