Interest Rate Calculator
Work out the interest rate needed to grow a sum of money to a target amount over a given period.
Enter Details
Required Annual Rate
7.461%
Simple Interest Rate
8.333%
Total Growth
25.00%
Total Interest
£2,500.00
How to Calculate the Required Interest Rate
Sometimes you know where you want to end up financially but need to work out what rate of return is required to get there. This calculator solves for the interest rate given a starting amount, a target amount, and a time period — the reverse of a standard compound interest calculation.
The formula used is: r = n × ((A/P)^(1/(n×t)) − 1), where A is the final amount, P is the principal, n is the compounding frequency, and t is the time in years. This gives the nominal annual interest rate required to achieve the target.
This is particularly useful for investors evaluating whether a particular investment opportunity is realistic. If you need a 15% annual return to meet your goal but the investment only offers 8%, you may need to extend your timeline, increase your starting capital, or adjust your target.
Frequently Asked Questions
What is the difference between nominal and real interest rate?
The nominal rate is the stated rate before adjusting for inflation. The real rate is the nominal rate minus the inflation rate, representing the actual increase in purchasing power.
What compounding frequency should I use?
Use monthly for savings accounts and mortgages. Use annually for long-term investment projections. Daily compounding gives the highest effective rate.
Is a higher interest rate always better?
For savings and investments, yes. For loans and credit, a lower rate is better. The key is always to compare the rate against your alternatives and the risk involved.
What is a realistic investment return?
A diversified equity portfolio has historically returned 6–10% per year over the long term. Savings accounts currently offer 3–5%. Returns above 15% per year are possible but carry significantly higher risk.