Reverse Compound Interest — Work Backwards
Traditional compound interest calculators tell you how much you'll have. This reverse calculator tells you what you need. Specify your financial goal amount and solve for the required starting principal, the interest rate needed, or the time required to reach your target.
The Mathematics Behind It
For Required Principal: P = A / (1 + r/n)^(nt). For Required Rate: r = n × [(A/P)^(1/(nt)) - 1]. For Required Time: t = ln(A/P) / (n × ln(1 + r/n)). Where A = target amount, P = principal, r = annual rate, n = compounds per year, t = time in years.
Planning Your Financial Goals
Want $1,000,000 in 20 years at 7% compounded monthly? You need $249,563 today. Can't invest that much? You'd need a 12.2% annual return to turn $100,000 into $1M in 20 years. Or at 7%, you'd need 33.4 years. This calculator helps you find the right balance between these variables.