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 |
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
Benchmarks
The calculator is a decision aid, not a fixed rule. Use the output to compare scenarios and document your assumptions.
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
Results are estimates for quick planning and should be checked before important financial, legal, tax, health, or business decisions.
May 25, 2026
Toolkit Shelf. Compound Interest Calculator. Retrieved May 25, 2026, from 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.