Investment Calculator: Formula and Examples
Project an initial investment and any monthly additions over time.
How the calculation works
The annualized return is converted to an equivalent monthly return. Beginning-of-month deposits earn one more monthly growth period than end-of-month deposits.
Investment formula
Monthly growth factor = (1 + annualized return)^(1 ÷ 12). Apply the factor and monthly investment for each month.
Worked example
At 0%, an initial $10,000 plus $200 monthly for 10 years totals $34,000.
Inputs, assumptions, and interpretation
Amounts and rates apply only to the defined scenario. For projections, returns remain constant and timing follows the selected input. Taxes, market variability, and unentered costs are excluded.
Displayed values are rounded, while calculations use unrounded numbers. The charts show modeled values rather than historical performance. For background, see Investor.gov introduction to investment returns.
Frequently asked questions
Are the default rates guaranteed?
No. Default inputs illustrate how the calculation works. Enter rates and contribution amounts relevant to your scenario, and review the applicable account or scheme terms.
Why might an actual statement differ?
Actual payment dates, compounding conventions, changing returns, fees, tax treatment, and account rules can differ from a simplified projection.
How should I interpret a negative result?
Some comparisons or value changes can be negative, including investment losses or a gap between alternative scenarios. Read the result labels to distinguish a balance from a change in value.