Investment Calculator
Investment projection assumptions
Project a portfolio using an initial balance, regular end-of-month contributions, and a constant annual return compounded monthly. The result separates contributions from estimated gains.
Formula and method
Future value = principal growth + future value of monthly contributions. A zero return produces the exact sum of the initial balance and contributions.
Worked example
$10,000 plus $500 per month for 10 years at an assumed 8% annual return grows to roughly $113,700, depending on contribution timing and rounding.
How to interpret the result
This is a scenario model, not a market forecast. Compare several return assumptions and pay attention to the share of the ending value supplied by contributions. A projection that only works at an unusually high constant return is more fragile than one supported by a realistic savings rate and a longer horizon.
Important limitations
- Market returns are variable and losses are possible.
- Fees, taxes and inflation are not included. This is educational, not investment advice.
Common questions
Why are returns shown as smooth growth?
The formula applies one constant monthly rate. Real investments rise and fall, and the order of returns affects outcomes when money is added or withdrawn.
Are contributions made at the start or end of the month?
They are modeled at the end of each month. Beginning-of-month contributions would receive one extra compounding period and produce a modestly higher result.
Source and further reading
Investor.gov compound interest calculator
Related tools
Method and examples reviewed September 8, 2026.