Compound interest calculator (with multipliers)
GCSE and IGCSE questions expect the multiplier method, not repeated addition. Enter the starting amount, the percentage rate per period and the number of periods, and this calculator shows the multiplier, the power calculation, the final amount and the total interest — plus a year-by-year breakdown you can check against your own working.
Compound growth and depreciation
2375.37
Multiplier: 1.035
Total interest earned: 375.37
Working
- Multiplier = 1 + 3.5 ÷ 100 = 1.035
- Final amount = 2000 × 1.035^5 = 2375.37
- Total interest = 2375.37 − 2000 = 375.37
Year by year
| Period | Value | Change |
|---|---|---|
| 1 | 2070 | 70 |
| 2 | 2142.45 | 72.45 |
| 3 | 2217.44 | 74.99 |
| 4 | 2295.05 | 77.61 |
| 5 | 2375.37 | 80.33 |
The method behind it
- Multiplier = 1 + r/100 (less than 1 when the rate is negative).
- Final amount = P × multiplierⁿ.
- Total interest or loss = final amount − P.
How to use this tool
1. Enter the starting amount
This is the principal — the money invested, the population, or the value of the item before growth or depreciation.
2. Enter the rate and periods
Type the percentage per period (use a negative rate for depreciation or decay) and how many periods the growth runs for.
3. Read the multiplier working
Check the multiplier and the power calculation — that single line is what earns method marks in the exam, even if your arithmetic slips.
Frequently asked questions
What is the formula for compound interest?
Final amount = P × (1 + r/100)ⁿ, where P is the starting amount, r is the percentage rate per period and n is the number of periods. Total interest is the final amount minus P.
How do you calculate depreciation?
Use the same formula with a negative rate, so the multiplier is less than 1. A car losing 15% a year has a multiplier of 0.85, so after 3 years its value is P × 0.85³.
What is the difference between simple and compound interest?
Simple interest is calculated on the original amount every period, so it grows by the same cash amount each time. Compound interest is calculated on the running balance, so the growth increases each period.
How do I find the number of years to reach a target?
Increase the number of periods in the table until the final amount passes your target — the year-by-year breakdown makes the first year over the threshold easy to read off. That trial approach is exactly what GCSE mark schemes accept.
Practise this properly, not just once
A solver gives you the answer; exam marks come from the working. MathsGradeUp pairs exam-board questions with step-by-step feedback and revision notes on the exact topics you keep dropping marks on.