About this Investment Growth Calculator
Project the long-term value of your investments using compound interest. Enter starting balance, monthly contribution, expected return, and time horizon. The inflation field shows your future balance in today's purchasing power.
Why time matters more than amount
Two investors save $300/month at 7%. Investor A starts at 25 and stops at 35 ($36K total). Investor B starts at 35 and contributes for 30 years ($108K total). Investor A ends up with more. Early dollars get the most compounding cycles.
Realistic return expectations
The S&P 500 has averaged ~10% nominal annually since 1928, or ~7% after inflation. Use 7% as a planning baseline. A 60/40 stock/bond portfolio averages 5–6%. Don't model 12%+; that requires luck or unusual concentration.
Frequently Asked Questions
What's a realistic annual investment return?
Plan on 6–8% real (after inflation) for a stock-heavy portfolio over the long term. 7% is a reasonable middle estimate. Anything above 10% over decades requires luck or unusual risk.
How much should I invest each month?
A common goal is 15–20% of gross income, including any employer 401(k) match. Even $50 monthly grows meaningfully over decades — start where you can and raise it with each raise.
Does the calculator account for taxes?
No — it shows pre-tax growth. Holding investments in a Roth IRA or 401(k) shields most of it; in a taxable brokerage, expect to give up 15–20% of long-term gains to capital gains tax.