Snowballr provides financial education, not investment advice. Verify any advisor on FINRA BrokerCheck.
Inverse calculator · Solves for monthly contribution

How much to invest per month to reach your goal

Standard compound interest calculators ask: given my monthly contribution, what do I end up with? This one flips it: given my target, what monthly contribution do I need? Set a goal — $500K, $1M, $2M — and the calculator solves the future-value-of-annuity formula backwards.

Quick answers to the most-asked goals

Reach $1 million in 30 years
$820/month at 7% nominal · $442/month at 10% · $1,202/month at 5%
Reach $1 million in 25 years
$1,234/month at 7% · $754/month at 10% · $1,679/month at 5%
Reach $1 million in 20 years
$1,920/month at 7% · $1,317/month at 10% · $2,433/month at 5%
Reach $500K in 30 years
$410/month at 7% · $221/month at 10% · $601/month at 5%
Reach $500K in 15 years
$1,577/month at 7% · $1,206/month at 10% · $1,871/month at 5%
Reach $250K in 20 years
$480/month at 7% · $329/month at 10% · $608/month at 5%

The math (closed-form, solvable on paper)

The future-value-of-annuity formula gives the final balance from a series of monthly contributions:

FV = P × (1 + r/n)^(n×t)  +  PMT × [((1 + r/n)^(n×t) − 1) / (r/n)]

Solving for PMT (the monthly we want):

PMT = [FV − P × (1 + r/n)^(n×t)] / [((1 + r/n)^(n×t) − 1) / (r/n)]

Where:
  FV  = target balance (your goal)
  P   = principal (starting amount, often $0)
  r   = annual rate as decimal
  n   = 12 (monthly compounding)
  t   = years

Same closed-form math as the Investor.gov (SEC) compound interest calculator — just rearranged to solve for PMT instead of FV.

Frequently asked questions

How much do I need to invest per month to reach $1 million in 30 years?
With $0 starting principal, month-end deposits and monthly compounding, about $820 per month reaches $1 million in 30 years at a constant 7% nominal rate. At 10% the illustration is about $442 per month; at 5% it is about $1,202. These are assumptions, not forecasts; include fees, taxes, inflation and market risk in a real plan.
How much do I need to invest per month to reach $500K in 20 years?
With $0 starting principal and month-end deposits, about $960 per month reaches $500,000 in 20 years at 7% nominal. At 8%, the illustration is about $849 per month. The same target over 30 years is about $410 per month at 7%; changing the horizon changes the result substantially.
What return rate should I assume?
There is no universally correct rate. Enter a clearly labelled nominal or real scenario that matches the account and time horizon, then compare lower and higher assumptions. Historical returns do not predict future results, and taxes, fees, inflation and contribution timing change the required amount.
What if I'm starting late (already 40 or 50)?
Starting later generally means a higher monthly contribution under the same assumptions. For a $1 million target at a constant 7% nominal rate, the month-end illustrations are about $3,155/month over 15 years, $1,234 over 25 years and $555 over 35 years, starting from $0. Use your actual horizon, starting balance and account terms in the calculator.
How much to be a millionaire starting from $0?
With $0 starting, month-end deposits and a constant 7% nominal rate, the illustration is about $820/month over 30 years, $555/month over 35 years and $1,920/month over 20 years. The result is a mathematical scenario, not a promise of investment performance.
Does this account for inflation?
The calculator applies the rate you enter and does not automatically inflate the target. To model today's purchasing power, use a real rate and label the target in today's dollars; at a constant 4% real rate, $1 million over 30 years is about $1,441/month from $0 with month-end deposits. Inflation assumptions should be tested rather than treated as fixed.

Related calculators

Educational tool. Past returns do not predict future returns. Math validated against Shiller's S&P 500 dataset and the SEC's Investor.gov calculator. Verified 2026-09-23.