Investment Growth Calculator

FV = PV(1+r)^n + PMT × [((1+r)^n - 1) / r]

This is the future value formula with regular contributions, the standard equation for projecting investment growth over time with compound interest.

What each variable means:

• FV is Future Value, the total your investment will be worth
• PV is Present Value, your initial lump-sum investment
• r is the periodic rate, meaning the annual rate divided by 12 for monthly compounding
• n is the total number of compounding periods, so years multiplied by 12
• PMT is your regular monthly contribution

When to use this calculator: Use it to project how savings or investments grow over time. It suits retirement planning, education funds, or any long-term goal you contribute to regularly.

Practical example: You invest $10,000 today and add $500 per month at 7% annual return for 20 years.

• Total contributions: $10,000 + ($500 × 240 months) = $130,000
• Final balance: $300,851
• Interest earned: $170,851

The interest is larger than everything you put in, and that crossover is the whole argument for starting early. It happens somewhere around year 17 in this example. Run it for 25 years instead of 20 and the balance reaches $462,290, so those five extra years add $161,000, more than the whole first decade produced.

A note on monthly compounding. This calculator compounds monthly, which is the convention for contribution-based projections and matches how most brokerage accounts actually behave. A calculator that compounds annually on the same inputs will return a slightly lower number, usually 1-2% less over long horizons. Neither is wrong; they answer marginally different questions. If you are comparing this against another tool and the figures differ by a percent or two, that is almost always why.

Tips:

• The US stock market has returned roughly 7-10% a year over long periods, before inflation and with wild variation between any two specific years. Nothing here is guaranteed.
• Small monthly contributions matter more than they look. $500 a month is $130,000 of contributions over 20 years and $300,851 of balance.
• Starting five years earlier usually beats contributing more later, because the early money compounds for the longest.
• The result separates contributions from interest so you can see how much of the balance you actually earned rather than deposited.