Investment Calculator
Project how an investment grows with compound interest and regular contributions, and what it's worth after inflation.
How it works
The calculator simulates your balance month by month. Your annual rate is converted to an effective monthly rate that matches your chosen compounding frequency, so annual, quarterly, monthly and daily compounding are all modeled exactly.
Contributions can be added at the start or end of each period. Start-of-period deposits earn one extra period of growth.
Add an inflation rate to see the future value in today's dollars. The chart and table split each year's balance into contributions and growth.
Formula
i
Where:
- n
- = Compounding periods per year (1, 4, 12, 365)
- i
- = Effective monthly rate
- C
- = Contribution for that month
- B
- = Balance
Worked example
$10,000 invested at 7% compounded annually for 10 years with no additions grows to 10,000 × 1.07^10 = $19,671.51.
$100 a month at 6% compounded monthly for 10 years (deposited at the end of each month) grows to $16,387.93 from $12,000 of contributions.
The Multiplier Effect of Compounding
The true power of investing lies not just in the amount you contribute, but in how frequently your earnings are reinvested to earn even more. While most people focus on the annual return rate, the compounding frequency, whether interest is added daily, monthly, or annually, can noticeably shift the final outcome over several decades. This calculator allows you to model these different frequencies exactly, showing how the 'effective' rate might differ from the nominal annual percentage rate. Even a small difference in compounding can lead to thousands of dollars in extra growth over a 30-year horizon.
Another vital consideration is the timing of your contributions. Depositing money at the start of a month rather than the end gives that capital an extra 30 days of growth in every single period. Over time, this 'extra' month of compounding on every contribution creates a snowball effect that significantly boosts the future value of your portfolio. Our tool allows you to toggle between start-of-period and end-of-period timing so you can see the tangible benefits of investing as soon as you receive your paycheck.
Accounting for Inflation
A million dollars sounds like a lot, but its purchasing power will be vastly different 20 or 30 years from now. One of the most important features of this investment tool is the inflation adjustment. By entering an assumed annual inflation rate, you can see your future balance expressed in 'today’s dollars.' This 'real value' helps you plan for actual expenses like housing and healthcare, providing a more grounded perspective on whether your current savings rate is truly sufficient to maintain your desired lifestyle in the future.
Frequently asked questions
Long-run US stock returns have averaged roughly 7% a year after inflation and about 10% before, but past returns don't guarantee future results.
Related calculators
For informational purposes only. This calculator does not provide financial advice. Consult a qualified professional before making decisions based on these results.