What this calculator does
This tool projects how much a savings or investment account will grow when you start with an initial balance and add a fixed amount on a regular schedule. It combines two effects: compound growth on money already in the account, and compound growth on each new contribution from the moment it is deposited. The result is the estimated future value at the end of your chosen time horizon.
How to use it
Enter your initial balance, the amount you contribute each period, the annual interest rate as a percentage, the number of years, and how often you contribute (monthly, quarterly, or annually). The calculator converts the annual rate into a periodic rate and assumes contributions are made at the end of each period (an ordinary annuity).
The formula explained
The future value is calculated as:
$$FV = PV(1+r)^n + PMT\dfrac{(1+r)^n - 1}{r}$$
Here PV is your starting balance, PMT is each contribution, r is the periodic interest rate (annual rate divided by contribution frequency), and n is the total number of periods (years × frequency). The first term grows your initial lump sum; the second term is the future value of a stream of equal payments.
Worked example
Suppose you start with $1,000, add $200 every month, earn 6% annually, and save for 10 years. The monthly rate is \(0.06/12 = 0.005\) and the number of periods is \(120\). The initial balance grows to about $1,819, and the contributions grow to about $32,776, for a total of roughly $34,595.
FAQ
Does it assume contributions at the start or end of the period? The end of each period (ordinary annuity), which is the most common convention for savings plans.
What if the interest rate is 0%? The calculator simply adds your initial balance to the sum of all contributions.
Is this guaranteed? No. It is a projection based on a constant rate. Real investment returns vary year to year and may be negative.
