Compound Interest Calculator - Growth With Contributions
See how savings grow when interest earns interest. Choose any compounding frequency, add regular contributions, and read the year-by-year breakdown.
Nominal yearly rate before compounding.
Year-by-year growth
| Year | Starting balance | Contributions | Interest | Ending balance |
|---|---|---|---|---|
| 1 | 10,000.00 | 6,000.00 | 1,054.96 | 17,054.96 |
| 2 | 17,054.96 | 6,000.00 | 1,640.52 | 24,695.47 |
| 3 | 24,695.47 | 6,000.00 | 2,274.68 | 32,970.15 |
| 4 | 32,970.15 | 6,000.00 | 2,961.47 | 41,931.62 |
| 5 | 41,931.62 | 6,000.00 | 3,705.27 | 51,636.89 |
| 6 | 51,636.89 | 6,000.00 | 4,510.80 | 62,147.68 |
| 7 | 62,147.68 | 6,000.00 | 5,383.19 | 73,530.87 |
| 8 | 73,530.87 | 6,000.00 | 6,327.99 | 85,858.86 |
| 9 | 85,858.86 | 6,000.00 | 7,351.21 | 99,210.07 |
| 10 | 99,210.07 | 6,000.00 | 8,459.35 | 113,669.42 |
Results assume a constant rate of return and that every contribution is made on schedule. Real investments fluctuate, and fees, taxes and inflation all reduce what you actually keep.
What is a Compound Interest Calculator?
Simple interest pays you only on your original deposit. Compound interest pays you on the deposit and on all the interest already credited, so the base you earn on keeps growing. The effect is small in year one and dominant by year twenty — which is why the compound interest formula is the single most useful piece of arithmetic in personal finance.
A = P × (1 + r ÷ n)n × t
Where P is the principal, r the annual rate as a decimal, n the number of compounding periods per year, and t the number of years. Add regular contributions and a second term is layered on top — the future value of an annuity — which this calculator handles for you.
Why Compounding Frequency Matters (a Little)
More frequent compounding means interest starts earning interest sooner. At a nominal 8% a year, the effective annual return is 8.00% compounded yearly, 8.16% half-yearly, 8.24% quarterly, 8.30% monthly and 8.33% daily. Continuous compounding — the theoretical limit — gives 8.33% too. The differences are real but modest; the rate and the time horizon matter far more.
- Seven compounding options from annual to continuous
- Monthly, quarterly or yearly contributions
- Choose start-of-period or end-of-period contributions
- Effective annual rate (APY) shown alongside the nominal rate
- Rule of 72 doubling time
- Year-by-year table separating contributions from interest
Common Use Cases
Savings Accounts
Project a deposit account or fixed-term product.
Investment Growth
Model a portfolio with regular monthly additions.
Education Fund
Work out what to save now for university in 15 years.
Comparing Accounts
Use APY to compare products that compound differently.
Savings Goals
Test how much monthly saving reaches your target.
Teaching Finance
Demonstrate compounding to students visually.
How to Use the Calculator
- Enter your starting principal.
- Enter the annual interest rate and how often it compounds.
- Set the time period in years.
- Add a regular contribution and choose its frequency.
- Tick start-of-period if you contribute at the beginning of each month.
- Read the future value, total interest, and the year-by-year table.
Nominal Rate, Effective Rate and the Rule of 72
A nominal rate is the headline figure a bank quotes. The effective annual rate — often labelled APY — is what you actually earn once compounding is included, calculated as (1 + r ÷ n)n − 1. Always compare products on effective rates, because two accounts advertising 6% can pay materially different amounts.
For a quick mental estimate, the rule of 72 says money doubles in roughly 72 ÷ rate years. At 6% that is 12 years; at 9%, 8 years. It is an approximation, but accurate enough for rates between about 4% and 12%.
Time Is the Variable That Matters Most
Because growth is exponential, the last years of a long horizon contribute far more than the first. Someone saving 500 a month at 8% from age 25 ends up with dramatically more than someone saving the same amount from age 35 — not twice the contributions, but many times the final interest. Run both scenarios in the calculator and the year-by-year table makes the gap obvious.
What the Projection Ignores
The output is nominal and assumes a constant rate. Inflation reduces what the final amount will buy, management fees compound against you exactly as returns compound for you, and any tax on interest or gains reduces the net result. For profit-sharing or Sharia-compliant products the expected rate is an expectation, not a guarantee — treat the figure as an illustration.
Who This Calculator Is For
- Savers comparing deposit accounts
- Long-term investors projecting portfolio growth
- Parents planning an education fund
- Anyone setting a savings goal with monthly contributions
- Finance students and teachers
- Advisers preparing client illustrations
❓ Frequently Asked Questions
What is compound interest?
Compound interest is interest earned on both your original principal and on the interest already added. Because the base keeps growing, the growth accelerates over time.
What is the compound interest formula?
A = P × (1 + r ÷ n)^(n × t), where P is the principal, r the annual rate as a decimal, n the number of compounding periods per year and t the number of years.
How does compounding frequency affect returns?
More frequent compounding produces slightly more interest. At 8% a year, annual compounding yields 8.00% while monthly yields 8.30% and daily 8.33% as an effective annual rate.
What is the effective annual rate (APY)?
It is the true yearly return once compounding is included, calculated as (1 + r ÷ n)^n − 1. It lets you compare accounts that quote the same nominal rate but compound differently.
What is the rule of 72?
Divide 72 by the annual interest rate to estimate how many years it takes for money to double. At 8%, that is roughly 9 years.
Can I include regular contributions?
Yes. Add a monthly, quarterly or yearly contribution and choose whether it is paid at the start or the end of each period — start-of-period contributions earn one extra period of growth.
Does continuous compounding make a big difference?
Very little in practice. Continuous compounding uses A = P × e^(rt) and at 8% gives an 8.33% effective rate, essentially the same as daily compounding.
Does the calculator account for inflation and tax?
No. The output is a nominal figure. Real purchasing power will be lower once inflation, fees and any tax on returns are taken into account.
Is this suitable for Islamic savings products?
You can model an expected profit rate the same way, but profit-sharing products do not guarantee a fixed return, so treat the result as an illustration only.
Is my data stored?
No. Everything runs in your browser and no figures are transmitted.