Money Calculators
Use this compound interest calculator to estimate future savings from a starting balance, monthly contribution, annual return, and time horizon.
Live calculator
Projected balance after monthly compounding.
Future value minus your starting amount and contributions.
Starting amount plus all monthly contributions.
Contributions add up to $40,000. The difference between that and the projected balance is estimated compounding growth: $23,368.
Long timelines show the first years and final year.
| Year | Contributions | Interest | Balance |
|---|---|---|---|
| Year 1 | $13,000.00 | $821.05 | $13,821.05 |
| Year 2 | $16,000.00 | $1,918.32 | $17,918.32 |
| Year 3 | $19,000.00 | $3,311.78 | $22,311.78 |
| Year 4 | $22,000.00 | $5,022.85 | $27,022.85 |
| Year 5 | $25,000.00 | $7,074.48 | $32,074.48 |
| Year 10 | $40,000.00 | $23,367.82 | $63,367.82 |
Use this as a planning estimate. Taxes, fees, rates, account terms, provider policies, local rules, and timing can change real-world results.
Quick answer
Compound Interest Calculator calculates future value from principal, contribution, rate, and years. The visible formula is Future value = principal x (1 + r)^n + monthly contribution x (((1 + r)^n - 1) / r), where r is monthly return and n is months.
Formula
Future value = principal x (1 + r)^n + monthly contribution x (((1 + r)^n - 1) / r), where r is monthly return and n is monthsThis calculator assumes monthly compounding, steady end-of-month contributions, and a constant annual return.
How to use
Example
Calculator use
Before relying on it
Details
These notes make the assumptions explicit, especially where the same search query can mean slightly different things.
The calculator assumes monthly compounding and end-of-month contributions so the projection stays simple and repeatable.
The annual return is an input, not a forecast. Investments can fall, and savings account rates can change.
Small changes in return assumptions can create large differences over long periods, so it helps to compare conservative and optimistic cases.
Source notes
Benchmarks
The calculator is a decision aid, not a fixed rule. Use the output to compare scenarios and document your assumptions. Benchmark ranges are broad planning heuristics unless this page names a specific source for the range.
Over a few years, the monthly amount you save usually matters more than the return assumption.
The longer the timeline, the more sensitive the result becomes to the return assumption.
Run a lower-return case too so the plan is not built around one optimistic number.
Calculator accuracy
The formula, inputs, example, and limitations are shown so the result is checkable, not just a number in a box.
Future value = principal x (1 + r)^n + monthly contribution x (((1 + r)^n - 1) / r), where r is monthly return and n is months
Principal, Contribution, Rate, Years
Money results are planning estimates. Actual taxes, account terms, rates, fees, timing, local rules, and provider policies can change the real-world result.
June 6, 2026
Toolkit Shelf. Compound Interest Calculator. Last reviewed June 6, 2026. https://toolkitshelf.com/tools/compound-interest-calculator
FAQ
Compound interest means interest can earn more interest over time, so growth can accelerate as the balance gets larger.
Yes. The calculator adds the monthly contribution at the end of each month and then shows total contributions versus growth.
No. It is a projection from the return you enter. Investments can go up or down, and cash accounts can change rates.
The table shows when growth starts to become meaningful compared with contributions, which is often easier to understand than one final balance.
No. Use it for planning and comparison. Real decisions can change after exact rates, balances, fees, taxes, account terms, timing, and personal details are verified.
Small changes in rates, payment timing, taxes, fees, balances, or income can materially change the result, so the assumptions need to stay visible.