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Free Calculator

Investment Interest Calculator

Free to use, runs entirely in your browser — no email, no signup.

The purpose of this Investment Interest Calculator is to illustrate the growth of savings and savings that you contribute to on a regular basis can grow. It also takes into account taxes and inflation. You can see over time if your “Buying Power” has increased or decreased after interest, taxes and inflation.

If your Buying Power Balance is lower than your Total Principle then you have essentially lost money and it may not be an investment you want to make.



Tutorial for the Investment Interest Calculator below.

Input & Results

Watch the video above for a complete explanation of the Input fields and how to understand the Results.


Breakdown

Monthly Accumulation Schedule

Yearly Accumulation Schedule

How we calculate growth

This calculator compounds your annual return monthly using (1 + rate)1/12 − 1, so your balance grows to exactly the annual rate you entered — no more, no less.

If another calculator shows a different number, it likely uses rate ÷ 12 instead, which compounds to a little more than the rate you typed and can overstate growth. For investment projections we use the effective-annual method on purpose so the results are not inflated. (Note: our debt calculators correctly use APR ÷ 12 instead, because that is how lenders actually charge interest — the right convention is different for money you owe versus money you grow.)