Compounding & Time
Start with one and rate to see why each year's interest can grow.
Predict, then watch
Why does the same 10% earn more later?
What did you just see?
The longer the period, the more periods earlier gains have to grow.
Rate and period assumptions
r is the and m is compounding periods per year. The periodic rate r ÷ m is converted to an equivalent monthly rate before each month-end contribution. The period t accepts whole years only, with 12 contributions per year. Scenario Comparison instead uses an effective annual return, so the inputs are not interchangeable.
Another example
- Enter an initial investment of 100,000 and a monthly contribution of 5,000.
- Set a 7% nominal annual return, 10 whole years, and monthly compounding.
- The result separates 700,000 of contributions from the modeled investment gain and final value.
Show formal definition and formula
Compounding reinvests prior interest or returns so future returns can earn returns of their own.
Final value equals the compounded initial principal plus the accumulated value of each monthly contribution.
Common mistakes
Do not treat a fixed return as guaranteed or confuse nominal and effective annual rates.
Frequently asked questions
When are monthly contributions added?
At month end, so the new contribution earns no interest for that month.
Is the nominal annual return guaranteed?
No. The calculator uses a constant assumption and cannot predict market fluctuations.
What changes with compounding frequency?
At the same nominal annual rate, more frequent compounding generally raises the effective annual return.
Why must the period be a whole number of years?
This tool adds one contribution at each month end and shows complete 12-month years. Whole years avoid ambiguity in partial-month contribution counts and yearly charts.
You can now explore…
- How earlier returns earn returns
- How contributions and gains change
Term reference4 terms
Open a term when you need a reminder. Underlined words in the article work too.