Calculate the future value of any investment or savings account with compound interest and monthly contributions. See how your money grows year by year with this free calculator.
Compounding, contributions & Rule of 72
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A future value calculator translates today's savings decisions into tomorrow's dollar amounts — which is exactly what retirement planning requires. If you invest $10,000 today at 7% annual return with monthly compounding, after 20 years it grows to roughly $40,000 without a single additional contribution. Add $300 per month and the same 20-year projection reaches over $195,000. Those numbers shift retirement planning from abstract to concrete, giving you a clear target and timeline rather than a vague goal to "save more."
Investment growth calculators are especially useful for visualizing the time cost of delay. A 25-year-old who invests $500/month at 7% for 40 years accumulates roughly $1.3 million by age 65. A 35-year-old starting the identical plan has only 30 years and ends up with about $608,000 — less than half, despite just 10 fewer years of contributions. The Rule of 72 makes this intuitive: at 7%, your money doubles every 10.3 years. Starting at 25 gives you roughly four doublings before retirement; starting at 35 gives you three. Each delay cuts your compounding power far more than the simple math of "10 years later" suggests.
Investing $5,000/year from age 25–35 (10 years, then stopping) builds more wealth by age 65 than investing $5,000/year from age 35–65 (30 continuous years). Time in market beats amount invested.
Regular contributions supercharge compounding. Adding $200/month to a $10,000 base at 7% for 25 years produces $202,000 — versus just $54,000 from the lump sum alone. Consistency builds the difference.
The difference between 6% and 8% annual return might seem small, but on $500/month over 30 years, it's the gap between $502,000 and $745,000. A single percentage point changes your retirement reality significantly.
Divide 72 by your annual return to estimate doubling time. At 6%, money doubles every 12 years. At 9%, every 8 years. Use this as a mental shortcut to evaluate any savings or investment growth projection quickly.
Future value projects what money invested today, plus anything added along the way, will be worth at a chosen date. Two components combine: the lump sum compounds on its own, while a series of regular contributions forms an annuity in which each deposit compounds for a different length of time — the first for the whole term, the last for barely any. This is why starting early beats contributing more later, and why the annuity term below has its own formula rather than being a simple multiple of the deposit.
FV = P(1 + r)^n + PMT × [ ((1 + r)^n − 1) ÷ r ]First term = growth of the lump sum; second = growth of the contributionswhere:
Assumptions: A constant return, contributions made on schedule at period end, and no tax or fees. Real markets deliver an average return through a sequence of very unequal years; the ending balance depends on that sequence as well as the average.
Start with $5,000, add $400 at the end of every month, and assume 7% a year compounded monthly.
Result$352,656 — from $125,000 of your own money
You contributed $5,000 + ($400 × 300) = $125,000; the remaining $227,656 is growth. Delaying the start by five years cuts the ending balance to about $229,000 — the lost years are the ones that would have compounded longest.