Finance
Compound Interest Calculator
Enter a starting balance, rate, compounding frequency, term, and optional deposits or withdrawals to model long-term growth.
Your details
Enter your details below
Your result
Based on the values you enter
Projection using your rates and contribution schedule; returns are not guaranteed.
Useful next checks
- Compare a few scenarios before making a decision.
- Check rates, fees, tax, and timing outside the estimate.
- Use the explanation below to understand the formula.
Intro
Use this compound interest calculator to estimate how savings or investments may grow over time. You can model a single starting investment, add regular deposits, include planned withdrawals, change how often interest compounds, and test annual increases to your contributions.
The result is designed for scenario planning. It shows the future balance, estimated interest, net contributions, effective annual rate, and a yearly breakdown so you can see how the balance builds.
What you can calculate
This calculator supports more than a simple starting balance and annual rate. Use it for questions such as:
- How much could a lump sum become after a chosen number of years and months?
- What difference would weekly, monthly, quarterly, or yearly deposits make?
- How does daily, monthly, quarterly, or annual compounding change the result?
- What happens if deposits increase each year?
- How much could regular withdrawals reduce the final balance?
- What effective annual rate does the selected compounding frequency create?
For goal-based saving, use the Savings Goal Calculator. For borrowing costs, compare the opposite side of compounding with the Loan Repayment Calculator or Mortgage Calculator.
Inputs explained
| Input | What it means |
|---|---|
| Initial investment | The amount already saved or invested at the start. |
| Interest rate | The nominal rate before the selected compounding effect is applied. |
| Rate period | Whether the rate you entered is annual, quarterly, monthly, weekly, or daily. |
| Compound frequency | How often interest is added to the balance. |
| Years and months | The length of the projection. |
| Regular contributions | Choose no regular movement, deposits, withdrawals, or both. |
| Deposit and withdrawal frequency | How often money is added or removed. |
| Contribution timing | Whether deposits or withdrawals happen before or after each monthly projection period. |
| Annual increases | Optional yearly percentage increases for deposits or withdrawals. |
If you choose Custom for compounding, the custom compounds-per-year field is used. Otherwise, the calculator uses the frequency selected in the compound frequency menu.
How the calculation works
The calculator first converts the entered rate into an effective annual rate using the selected compounding frequency:
Effective annual rate = (1 + r / n)^n - 1
In this formula, r is the nominal annual rate as a decimal and n is the number of compounding periods per year.
The calculator then projects the balance month by month. Regular deposits and withdrawals are converted into monthly equivalents from their selected frequencies, adjusted for any annual increase, and applied either at the beginning or end of the projection period.
This monthly projection makes it possible to combine daily compounding with monthly deposits, quarterly withdrawals, or other mixed scenarios in one simple tool.
Example calculation
The worked examples on this page use US dollars (USD). Choosing UK - GBP changes the calculator's currency labels; it does not convert your entries or these examples.
Set the initial amount to $5,000, the interest rate to 5%, Rate period to Yearly, Compounding to Monthly, and the term to 5 years and 0 months. Choose Add deposits, enter $100 monthly, set the deposit increase to 0%, and choose End of each period. No withdrawals are included.
With a monthly rate i = 0.05 / 12 and 60 deposits, the balance is:
Future balance = 5,000 × (1 + i)^60 + 100 × ((1 + i)^60 - 1) / i = $13,217.40
| Part of the result | Amount |
|---|---|
| Starting savings | $5,000.00 |
| New deposits: $100 × 60 | $6,000.00 |
| Total money contributed | $11,000.00 |
| Interest earned | $2,217.40 |
| Estimated ending balance | $13,217.40 |
The first month earns $5,000 × 0.05 / 12 = $20.83 before the $100 deposit, leaving approximately $5,120.83. The effective annual rate is 5.12%, rounded from (1 + 0.05 / 12)^12 - 1.
Changing only Timing to Beginning of each period gives $13,245.74, about $28.34 more: each deposit earns one additional month of interest. This comparison assumes the same constant rate, deposit and term. The calculator keeps full precision during the projection and rounds displayed amounts to cents.
Compounding frequency and APY
The stated interest rate and the effective annual rate are not always the same. A 5% nominal annual rate compounded monthly produces a slightly higher effective annual rate because interest is added during the year and can itself earn interest.
The result panel shows the effective annual rate so you can compare scenarios more fairly. This is especially useful when comparing accounts or investments that quote similar headline rates but compound at different intervals.
Deposits, withdrawals, and timing
Regular deposits can make the biggest difference over long periods because each added amount has time to earn interest. Regular withdrawals work in the opposite direction: they reduce the balance available to compound.
Timing also matters. Contributions made at the beginning of a period start earning sooner than contributions made at the end. For most everyday savings scenarios the difference is modest, but it becomes more noticeable over longer terms or larger contribution amounts.
Assumptions and limitations
- The entered rate is assumed to remain constant for the whole term; 5% in the example is hypothetical, not a forecast or an account offer.
- The projection uses monthly periods, even when the selected compounding frequency is daily or yearly.
- Weekly and bi-weekly deposits are spread into monthly equivalents, rather than credited on exact calendar dates. A yearly deposit is also spread across the year in this model.
- Taxes, account fees, inflation, platform charges, and changing investment returns are not included.
- Withdrawals are capped at the available projected balance.
- The result is an educational estimate, not financial advice. Negative rates or withdrawals can reduce the balance; growth is not guaranteed.
Background reading
Investor.gov’s compound interest calculator explains the role of starting savings, contributions, time and compounding. The worked figures above use this page’s stated monthly timing assumptions.
Frequently asked questions
What is compound interest?
Compound interest means interest is added to the balance, so later interest can be earned on both the original money and earlier interest.
Does compounding frequency matter?
Yes. More frequent compounding can increase the effective annual rate, though the difference may be small at modest rates.
Can I include deposits and withdrawals together?
Yes. Choose deposits and withdrawals in the regular contributions field, then enter both amounts and frequencies.
Why does contribution timing change the result?
Money added at the beginning of a period has more time to earn interest than money added at the end.
Can I use this for investments?
Yes, as a simplified projection. Real investment returns vary and can be negative.
Can I include regular deposits or withdrawals?
Yes. Choose deposits, withdrawals, or both, then enter the amount, frequency, timing, and any annual increase.
What is the effective annual rate?
The effective annual rate shows the annual growth rate after the selected compounding frequency is included.
Are the results guaranteed?
No. The result is an estimate based on the values entered and does not account for fees, taxes, inflation, or market changes.