Simple interest calculator
Fill in what you know and leave the unknown box empty — it works out whichever one is missing. Nothing is uploaded; the arithmetic happens in your browser.
The formula
I = P × r × t
Where this usually goes wrong
Rate as a decimal, not a percent: 5% is 0.05. Time in the same unit the rate is quoted per, normally years.
Worked example
$1,200 at 5% for 3 years earns $180.
Those numbers are already in the boxes above — press Work it out to see it, then change them for your own.
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