Total contributed: 12,000
100 × 12 × 10 = 12,000
There are 120 monthly contributions. This total is the money you put in yourself, including the initial deposit of zero. It excludes interest.
Saving and growth
Compound Interest Calculator
Estimate how a deposit grows with a fixed interest rate and regular additions.
Enter a deposit and compounding schedule
Estimated future value
Enter your deposit, annual rate, and years, then select Calculate.
All amounts use the same currency as your inputs.
- Total contributed, including initial deposit
- Total interest earned
View annual breakdown
| Year | Balance | Contributed | Interest |
|---|
Amounts are shown to 2 decimal places. ≈ marks rounding. Fractional cents are retained between periods; an account that rounds posted interest can have a different balance.
Calculated in your browser. This fixed-rate estimate excludes taxes, fees, inflation, and withdrawals; it does not guarantee future returns.
Read a monthly savings projection
Suppose you start from zero and set aside 100 at the end of every month for 10 years. To model a fixed 5% nominal annual rate, enter Initial deposit: 0, Nominal annual interest rate (%): 5, Years: 10, and Contribution each month: 100. Select Monthly · 12 times per year and End of each period.
Estimated future value: ≈ 15,528.23
Period rate = 5% ÷ 12
The result combines your deposits with interest accumulated over the 120 periods. Each deposit earns interest only after it arrives; the full 12,000 is not present for all 10 years.
Total interest earned: ≈ 3,528.23
15,528.23 − 12,000 = 3,528.23
Interest is the projected balance minus your contributions. The displayed future value is not all earnings: 12,000 of it came from your own deposits.
Open View annual breakdown to check the projection along the way. Year 1 shows a balance of approximately 1,227.89, with 1,200 contributed and approximately 27.89 in interest. Year 2 shows approximately 2,518.59, with 2,400 contributed and approximately 118.59 in interest. These are cumulative amounts from the start: the Year 2 interest figure includes the interest already earned in Year 1.
With end-of-period contributions, the last 100 is added after the final month's interest calculation, so it earns no interest within this projection. The estimate assumes every scheduled contribution is made and the nominal rate stays at 5%. Taxes, fees, inflation, and withdrawals are excluded; actual returns are not guaranteed.
Worked examples
1,000 at 5% for 10 years
1,000 × 1.05¹⁰ ≈ 1,628.89
With annual compounding and no added contributions, the deposit earns approximately 628.89 in interest. Interest is earned on both the deposit and the interest already accumulated.
Add 100 each year for 2 years at 5%
End: 1,307.50 · Beginning: 1,317.75
Start with 1,000. End-of-year additions give 1,307.50; beginning-of-year additions give 1,317.75. Both include 1,200 in total contributions, but the earlier deposits earn more interest.
1,000 plus 100 monthly for 2 years
1,000 + 100 × 24 = 3,400
At a 0% rate, the result is simply the initial deposit plus all 24 contributions. The balance is 3,400, and the timing of contributions has no effect.
Formula and assumptions
Let P be the initial deposit, C the contribution per period, r the nominal annual rate as a decimal, n the periods per year, and t the years. The period rate is i = r ÷ n, and the total number of periods is N = n × t.
With no contributions, future value is P × (1 + i)ᴺ. For end-of-period contributions and a nonzero rate, add C × [(1 + i)ᴺ − 1] ÷ i. For beginning-of-period contributions, multiply that contribution portion by (1 + i). At zero interest, use P + C × N. OpenStax explains the ordinary-annuity and annuity-due formulas for these two contribution schedules.
The calculator applies the equivalent period-by-period recurrence. At the end of each period, the balance becomes balance × (1 + i) + C for end contributions, or (balance + C) × (1 + i) for beginning contributions. Total contributed is P + C × N; interest earned is future value minus total contributed.
Years must be whole numbers from 1 to 50. Initial and recurring deposits accept up to two decimal places and a maximum of 1,000,000,000,000 each. The annual rate accepts 0–100%, with up to 10 decimal places. Annual, quarterly, and monthly periods are supported; calendar dates, variable rates, withdrawals, taxes, fees, and inflation are outside this model.
Decimal arithmetic uses 100 significant digits internally. Interest is not rounded to cents after each period. Displayed amounts use two decimal places, with exact halfway values rounded away from zero. The ≈ mark means the displayed amount was rounded; separately rounded totals can differ by a cent when added together. An actual account may use a different posting schedule or rounding rule.
The Consumer Financial Protection Bureau explains compound interest with an annual-compounding example. The SEC's Investor.gov calculator also illustrates how deposits, time, interest rates, and compounding affect growth. Compare assumptions before comparing results: this calculator matches contributions to the selected compounding period.
Common questions
Is the annual interest rate the same as APY?
No. This calculator takes a nominal annual rate and divides it by the number of periods per year. An effective annual yield already includes compounding. For example, 12% nominal interest compounded monthly gives a 1% period rate and an effective annual growth rate of about 12.68%, before any fees. Do not enter an APY as though it were the nominal rate.
Does changing monthly to annual compounding convert my contributions?
No. The number stays the same and its label changes. A contribution of 100 means 100 each month with monthly compounding, but 100 each year with annual compounding. If you intend to deposit 1,200 once per year, select annual and enter 1,200. A single annual deposit and twelve monthly deposits can still earn different interest because the money arrives at different times.
What changes between beginning and end contributions?
A beginning contribution is added before that period's interest. An end contribution is added after it. Over one year of monthly compounding, either option adds exactly 12 contributions. The beginning schedule starts with the first contribution alongside the initial deposit; the end schedule makes its last contribution at the end of the year.
Can I start with zero or leave the contribution blank?
Yes. A zero initial deposit lets you estimate growth from recurring additions. Leaving contributions blank uses zero, so only the initial deposit grows. A 0% rate is also accepted. Negative deposits, withdrawals, and negative interest rates are not part of this calculator.
Why might my bank's balance be different?
This is a projection using a fixed nominal rate and equal compounding periods, with no cent rounding between periods. Real accounts can calculate interest daily, post it on another schedule, change rates, or apply fees and taxes. Their calendar and rounding rules can change the outcome.
What does the annual breakdown show?
Each row is the balance at the end of that year. Contributed amounts include the original deposit and every recurring contribution up to that point. Interest is cumulative from the start, rather than just the interest earned in that particular year.