Interest Rate Calculator
$
$
10 yrs
Required Annual Rate7.18%
Present Value$10,000.00
Future Value$20,000.00
Sometimes you know where your money started, where you want it to end up, and how long you have, but not the rate that connects them. This calculator solves for exactly that: the annual interest rate required to grow a present value into a target future value over a set number of years. Choosing a compounding frequency lets the answer match how the account actually credits interest.
Formula
r = n · [ (FV / PV)^(1/(n·t)) − 1 ]
- r
- Required nominal annual rate (as a decimal before ×100)
- PV
- Present value (starting amount)
- FV
- Future value (target amount)
- n
- Compounding periods per year
- t
- Number of years
How it works
- Enter the present value (starting amount), the future value (target), the number of years, and the compounding frequency.
- The calculator inverts the compound growth formula to isolate the periodic rate, then annualizes it by multiplying by the number of compounding periods per year.
- The result is the nominal annual rate, as a percentage, that turns your present value into the future value over the chosen horizon at that compounding frequency.
Worked example
Doubling $10,000 to $20,000 in 10 years with annual compounding.
- Ratio: FV ÷ PV = 20,000 ÷ 10,000 = 2.
- With n = 1, exponent = 1 ÷ (1 × 10) = 0.1.
- Periodic growth: 2^0.1 ≈ 1.07177.
- Annual rate: 1 × (1.07177 − 1) × 100 ≈ 7.18%.
You would need about a 7.18% annual return to double $10,000 in 10 years.
Frequently asked questions
- How is this different from a regular interest calculator?
- A standard interest calculator knows the rate and finds the ending balance. This one works in reverse: it knows the starting and target balances plus the time, and solves for the rate that links them.
- Does compounding frequency change the required rate?
- Yes. More frequent compounding earns interest sooner, so a slightly lower nominal rate hits the same target. Selecting the frequency that matches your account gives the most accurate required rate.
- Why do I need positive present and future values?
- The formula divides the future value by the present value and raises it to a fractional power, which is only defined for positive amounts over a positive time span. If any input is zero or negative, the calculator returns zero.
- Is the result a guaranteed return?
- No. It is the constant annual rate that would be required to reach your goal. Real investments vary year to year, so treat the figure as a benchmark for what average return you would need, not a promise.