Opportunity Cost Calculator
See what an expense could become—and how it could change your FIRE date.
What expense do you want to compare?
Expense to compare
Adjust assumptions · 10 years · 7% return · 4% withdrawal
Invested value after 10 years
Money redirected
Estimated growth
What changes in the FIRE plan
$200 moves from monthly spending to monthly investing. Annual spending falls to $42,600 and monthly investing rises to $2,700.
Current path
173 months
Target $1,125,000
Redirect the expense
160 months
Target $1,065,000
How this comparison works
The alternative value applies a constant annual return converted to an equivalent monthly rate. Monthly amounts are invested at the end of each modeled month; a one-time amount is invested immediately.
For a recurring expense, the redirected plan assumes the expense is already included in annual spending. It lowers annual spending by 12 times the expense and raises monthly investing by the same amount. A one-time expense only changes invested assets.
FIRE targets use annual spending divided by the selected withdrawal rate. Returns, expenses, taxes, inflation, and withdrawal safety vary in real life, so projected months are illustrative estimates rather than forecasts. No inputs are saved unless you choose to open the redirected plan in the FIRE calculator.
Methodology reviewed: September 5, 2026.