Interest Calculator

Calculate compound interest with recurring contributions, tax, and inflation adjustments — plus a full accumulation schedule.

$
$
$
%
yr
mo
%
Reduces each period's earned interest
%
Used to calculate buying power
Enter your details and press Calculate

Calculate simple or compound interest instantly with our free interest calculator. See how much interest you'll earn or owe over any time period.

How Interest Is Calculated

Simple Interest: I = P × r × t.

Compound Interest: A = P(1 + r/n)^(nt), where P is principal, r is annual rate, n is compounding frequency per year, and t is time in years.

How to Use This Calculator

  1. Choose simple or compound interest
  2. Enter principal amount
  3. Enter interest rate and time period
  4. For compound, select compounding frequency
  5. Click Calculate

Frequently Asked Questions

What's the difference between simple and compound interest?

Simple interest is calculated only on the original principal. Compound interest is calculated on the principal plus any previously earned interest, so it grows faster over time.

Does compounding frequency matter?

Yes, more frequent compounding (daily vs annually) results in slightly higher returns for the same nominal rate.

Is this useful for both savings and debt?

Yes, the same math applies whether you're calculating interest earned on savings or interest owed on debt.

What rate should I use for a rough estimate?

Use the nominal annual rate stated by your bank or lender; check if it's compounded and how often for precise comparisons.