SMALL CONTRIBUTIONS. A LONGER VIEW.
Compound interest calculator
Test your starting balance, monthly contributions and a fixed return assumption. Compare your own contributions with growth, check purchasing power after inflation, and find the monthly saving needed for a target.
SAVINGS & INVESTING
Compound interest calculator
This is a mathematical projection, not a forecast or guaranteed return. No investment taxes, fees, withdrawals or varying market returns are modeled. Target is a future dollar amount.
What a different return changes
The same contribution plan under three fixed assumptions. These scenarios do not represent probabilities.
FOLLOW THE MATH
Your year-by-year projection
The first row is your starting position. A final partial year appears if the selected duration is not a whole number of years.
| Year | New contributions | Growth / loss | Total contributed | Future balance | Today’s purchasing power |
|---|
A worked example you can reproduce
Start with $10,000, add $200 at the end of each month for 10 years, and assume a 6% nominal annual rate compounded monthly. You contribute $34,000 in total. The projected balance is about $50,969.84, including $16,969.84 of growth.
With 2.5% annual inflation, that ending balance has approximately the purchasing power of $39,817.55 today. The inflation field changes this purchasing-power estimate; it does not subtract money from the nominal account balance.
Set the return to 0%: the ending balance becomes exactly $34,000. Move contributions to the start of the month: each new contribution earns one extra month of assumed return.
Formula, timing and limitations
Let P be the initial balance, C the monthly contribution, r the annual percentage rate divided by 1,200, and n the number of monthly periods. End-of-month balance is P × (1 + r)n + C × ((1 + r)n − 1) ÷ r. At zero return, use P + C × n. Start-of-month contributions multiply the contribution term by (1 + r).
Purchasing power equals future balance ÷ (1 + annual inflation rate)years. The target calculation solves the same compound formula for the required monthly contribution. The target is in future dollars; if you want a target expressed in today’s dollars, increase it for your own inflation assumption first.
- Durations are rounded to the nearest whole month; the result shows the exact monthly period count.
- Returns are constant hypothetical rates with monthly compounding. A bank’s APY, daily interest conventions or changing market returns may produce different results.
- Negative return assumptions model a fixed loss rate. They cannot describe the sequence or volatility of real investment returns.
- Contributions stay constant. There are no withdrawals, tax effects, platform fees or contribution limits in this general savings model.
- A zero-year duration gives the current balance. A larger target then requires more time; there is no finite monthly saving schedule at zero duration.
Reference: Investor.gov’s compound-interest planning resource. DailyToolDesk’s monthly model and controls are described above; outputs may differ from calculators using another frequency or timing convention. Software and worked example checked October 28, 2026.
Frequently asked questions
Is the projected growth guaranteed?
No. A fixed annual return is an input to the math. Real investment values can fall, and savings-account rates can change.
Why is the inflation-adjusted amount smaller?
Positive inflation means a future dollar buys less. The adjusted amount expresses the future balance in today’s purchasing power.
Can I save less if my target is already covered?
The required monthly contribution is shown as zero when the assumed growth of your starting balance reaches the target. This relies on the entered return assumption and does not guarantee the target will be reached.
Are my financial inputs stored?
This tool calculates in your browser without saving the inputs. Copy and download only create a result summary or file when you choose those controls.