Spend vs. Invest Fork Calculator
Example: Windfall amount: 100000 $ · Percent you plan to spend: 20 % · Expected annual investment return: 7 % · Investment horizon: 25 years
| Lifetime opportunity cost of spending | $108,549 |
| Future value (80% invested) | $434,195 |
| Future value if 100% invested | $542,743 |
| Amount spent today | $20,000 |
Worked example
A $100,000 inheritance with 20% spent ($20,000 on a trip) leaves $80,000 invested at 7% for 25 years, growing to $433,754. Had you invested the full $100,000, it would reach $542,743. The opportunity cost of that $20,000 trip is $108,989 in 2050 dollars — a choice worth knowing before you book the flight.
Frequently asked questions
Does this mean I should never spend any of a windfall?
Not at all. The fork calculator makes the cost visible so you can decide consciously. Many financial planners endorse enjoying 10–20% guilt-free; the key is knowing what each dollar truly costs over time.
What return rate should I use?
The S&P 500 has averaged roughly 7% annually after inflation over long periods (SEC investor.gov data). Use 5% for a conservative all-bond portfolio, 7–8% for a diversified stock/bond mix, or 10% for all-equities to see the full range.
Does inflation reduce the gap?
If you enter a real (inflation-adjusted) return rate, the results are already in today's dollars. If you enter a nominal rate, the gap is in future dollars — still real, just not deflated. The relative trade-off holds either way.
What if I invest the spent portion gradually over time instead?
Use the Lump-Sum vs Dollar-Cost-Average tool to model phased deployment. The fork calculator assumes immediate investment of the unspent portion, which is the simplest baseline.