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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
$880/month at 7% return · $440/month at 10% · $1,200/month at 5%
Reach $1 million in 25 years
$1,310/month at 7% · $700/month at 10% · $1,750/month at 5%
Reach $1 million in 20 years
$1,920/month at 7% · $1,150/month at 10% · $2,440/month at 5%
Reach $500K in 30 years
$440/month at 7% · $220/month at 10% · $600/month at 5%
Reach $500K in 15 years
$1,560/month at 7% · $1,140/month at 10% · $1,840/month at 5%
Reach $250K in 20 years
$480/month at 7% · $290/month at 10% · $610/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?
About $880 per month at a 7% real return. At 10% nominal return (S&P 500 historical), only about $440 per month. At 5% (conservative), you need $1,200 per month. The exact number depends on your assumed return rate and any starting principal — use the calculator above to plug in your specific numbers.
How much do I need to invest per month to reach $500K in 20 years?
About $960 per month at 7% return. At 8% return, $880/month suffices. The same $500K target in 30 years requires only $440/month at 7% — every extra decade of compounding roughly halves the required contribution.
What return rate should I assume?
For long-term diversified equity portfolios (S&P 500 index funds), the historical nominal return is about 10% per year and the real (after-inflation) return is about 7%. For balanced 60/40 stock/bond portfolios, use 6-7%. For bond-heavy or HYSA, use 4-5%. Most financial planners use 7% as a sensible middle estimate that bakes in some inflation buffer.
What if I'm starting late (already 40 or 50)?
Compound interest rewards time more than contribution amount, so starting later means much higher required monthly contributions. To reach $1M starting at age 50 (15 years to retirement) at 7% return, you need about $3,200/month. Starting at age 40 (25 years), about $1,300/month. Starting at age 30 (35 years), only $610/month. Time is the most powerful lever in personal finance.
How much to be a millionaire starting from $0?
With $0 starting, 7% annual return, and a 30-year horizon, you need to invest ~$880/month. Stretch to 35 years and it drops to $610/month. Compress to 20 years and it jumps to $1,920/month. The 'millionaire monthly number' is essentially a function of how many years you give compounding to work.
Does this account for inflation?
By default, no — this calculator gives nominal dollars. To plan in today's purchasing power, use a real return rate (subtract ~3% for typical US inflation). For example: 7% nominal minus 3% inflation = 4% real. A $1M target in today's dollars at 4% real return over 30 years requires ~$1,440/month. Use 4-5% as your rate input if you want results in today's dollars.

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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 2026-05-27.