Toolkit ShelfUse 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.
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
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
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
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.
Method and sources checked on July 13, 2026. The documented method, source timing, validity conditions, and reliance limits were checked on this date.
Toolkit Shelf. Compound Interest Calculator. 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.
Leave passwords, account numbers, and private medical or tax information out of your report.