A clearer view of your savings
Compound interest calculator.
Use this compound interest calculator to explore monthly contributions, compare compounding frequencies and understand how much of your future balance comes from you.
01 / Your savings plan
Small habits. Visible progress.
Explore an illustrative return, not a guaranteed outcome.
Labels only; no exchange-rate conversion.
Contributions always happen monthly. Fractional years must correspond to whole months (for example, 1.5 years = 18 months).
02 / Projected balance in 10 years
$9,998.32 projected interest on $22,000.00 of your deposits.
- Your deposits
- $22,000.00
- Interest earned
- $9,998.32
- Effective annual yield
- 5.116%
- Monthly deposits
- 120
What could regular contributions change?
- $0.00 / month
- $16,470.09
- $100.00 / month
- $31,998.32
- $200.00 / month
- $47,526.55
Same initial deposit, rate, duration and deposit timing.
Constant return with interest reinvested. Taxes, fees, inflation and market volatility are excluded. Equivalent monthly growth is used between compounding dates; actual bank day-count and crediting rules can differ.
03 / Explore your year-by-year growth
| Year | Your deposits | Interest earned | Balance |
|---|---|---|---|
| 1 | $11,200.00 | $539.50 | $11,739.50 |
| 2 | $12,400.00 | $1,168.01 | $13,568.01 |
| 3 | $13,600.00 | $1,890.06 | $15,490.06 |
| 4 | $14,800.00 | $2,710.44 | $17,510.44 |
| 5 | $16,000.00 | $3,634.20 | $19,634.20 |
| 6 | $17,200.00 | $4,666.60 | $21,866.60 |
| 7 | $18,400.00 | $5,813.23 | $24,213.23 |
| 8 | $19,600.00 | $7,079.91 | $26,679.91 |
| 9 | $20,800.00 | $8,472.79 | $29,272.79 |
| 10 | $22,000.00 | $9,998.32 | $31,998.32 |
At an illustrative 5% nominal annual rate compounded monthly for 10 years, a $10,000 initial deposit plus $100 at the end of each month grows to $31,998.32. That is $22,000.00 deposited and $9,998.32 projected interest, before tax, fees and inflation.
The compound interest formula
Without additional deposits, the compound interest formula is A = P × (1 + r/n)^(n × t). P is your starting principal, r is the nominal annual rate as a decimal, n is the number of compounding periods per year and t is time in years. The result A includes your principal; subtract P to find interest earned.
For $10,000 at 5% compounded monthly over 10 years, the balance is $16,470.09. A simple-interest calculation for the same principal, rate and duration would give $15,000. The difference comes from earning interest on previously accumulated interest.
Adding monthly contributions correctly
For end-of-month contributions, use the equivalent monthly rate i = (1 + r/n)^(n/12) − 1 and the number of months m:
A = P(1+i)m + C[(1+i)m − 1] ÷ i
C is one monthly contribution. For start-of-month contributions, multiply the contribution portion by (1+i). At zero interest, use P + C × m. This calculator simulates the same process month by month, making the deposit count explicit in the result.
The selected compounding frequency changes interest growth, not how often you contribute. The model uses equivalent growth within partial compounding periods. It does not reproduce a specific bank's posting calendar, leap-year calculation or balance eligibility rules.
Nominal interest rate versus APY and AER
A nominal savings rate is the rate before accounting for compounding. APY and AER are effective annual yields. For a nominal decimal rate r compounded n times a year, the effective annual yield is (1 + r/n)^n − 1. Enter an advertised APY or AER using the effective-yield option; applying another round of compounding to it would overstate growth.
Be careful with the term APR. In borrowing, APR can include fees as well as interest. A loan APR is not automatically the nominal deposit rate required by a savings formula. Compare like-for-like disclosures and check whether a quoted savings rate changes after an introductory period.
Daily, monthly, quarterly or annual compounding?
At the same positive nominal rate, more frequent compounding increases the effective yield. These examples use $10,000 at a 5% nominal rate for 10 years, with no further deposits.
| Compounding | Effective yield | Final balance |
|---|---|---|
| Annual | 5.000% | $16,288.95 |
| Quarterly | 5.095% | $16,436.19 |
| Monthly | 5.116% | $16,470.09 |
| Daily | 5.127% | $16,486.65 |
Turn the result into a useful comparison
Start with a contribution you can sustain and compare it with zero deposits and an additional 100 per month. Then change the return assumption to see how sensitive your plan is. A future investment return is uncertain, so one smooth growth curve should not be read as a forecast of market performance.
The balance is in today's selected currency units, without an inflation adjustment. If purchasing power is your question, continue to the inflation calculator. If you know the amount you need and want to work back to a savings plan, try the savings calculator. Download the monthly schedule to keep a record of the assumptions behind your scenario.
FAQ
Frequently asked questions
How do I calculate compound interest with monthly contributions? ▾
Should I enter a nominal rate, APY or AER? ▾
Does daily compounding mean I contribute every day? ▾
Can I start with no money or use a zero interest rate? ▾
Do beginning-of-month contributions earn more interest? ▾
What is the difference between compound and simple interest? ▾
Does the projection include inflation, fees or tax? ▾
Sources & Methodology
The interactive calculator and worked examples share one tested monthly simulation. Full precision is retained until display. Effective annual yields are converted to equivalent monthly growth without double-compounding.
- Investor.gov (SEC) — Compound interest calculator and planning inputs
- CFPB — Why a borrowing APR differs from an interest rate
Standards and figures reviewed 9 September 2026.