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.