Skip to content
Jon Curry

The Next Dollar · Calculator

Monthly Investment Needed Calculator

Work backward from a goal. Enter your current balance, a target amount, and a timeline, and see the constant monthly contribution that gets you there under one assumed rate of return.

Plan Backward From a Goal

Monthly Investment Needed Calculator

Zero login requiredNo signup, no paywall
$20,000
$0$250k$500k
$1,000,000
$50k$1.5M$3M
20 yrs
1y20y40y
7%
0%7%12%
Note on AssumptionsThis assumes one constant monthly contribution and one constant annual return for the entire time horizon, with no separate inflation adjustment. Real markets do not move in a straight line — treat this as a planning estimate, not a guarantee, and revisit it as your balance, timeline, or goal changes.
Required Monthly Contribution
$1,765/mo
Total Future Contributions
$423,503
over 20 years
Estimated Growth
+$556,497
56% from compounding
Projected final balance$1,000,000
Target amount$1,000,000
Growth Trajectory (0 to 20y)2.3× multiplier
$1,000kYr 0Yr 10Yr 20
Total balance (with growth)Your direct contributions
2.3× growth multiplier

Methodology & Math

Solving for the Monthly Contribution

This calculator rearranges the same future-value-of-annuity formula behind the Investment Growth Calculator, solving for the payment instead of the ending balance:

PMT = (FV − PV(1+r/n)^(nt)) × (r/n) / ((1+r/n)^(nt) − 1)

PV is your current balance, FV is your target amount, and the result is the constant contribution needed at the end of every month to close the gap, assuming the rate of return holds steady for the entire timeline. If your current balance alone is already projected to clear the target, the required contribution shows as $0 rather than a negative number.

One Assumption, Not a Forecast

This tool uses a single assumed annual return with no separate inflation adjustment, and it does not vary the return year to year the way real markets do. It is meant to answer a planning question — roughly how much would I need to set aside each month — not to predict what will actually happen. Whether the return you choose represents a nominal or inflation-adjusted assumption is up to you to decide and stay consistent about.

Back to The Next Dollar Hub