Purchase Impact Calculator

No. The calculator exists to give you full information, not to paralyze you. Some purchases are genuinely worth their FIRE cost — experiences, tools, things you'll use daily for years. The goal is to make spending decisions consciously, with awareness of the trade-off. You might decide that new car is worth 12 months of delay.

Opportunity cost is what you give up by choosing one option over another. In investment terms, every dollar spent is a dollar that won't compound. The calculator shows the future value of the purchase price — not to make you feel guilty, but to make the hidden trade-off visible.

The calculator runs two simulations starting from today: one with your current net worth, one with your current net worth minus the purchase price. It measures when each simulation crosses your FIRE number and reports the difference in months.

This calculator treats the purchase as a pure expense. For investments like real estate or index funds, use the Compound Interest Calculator instead. For most consumer goods (cars, electronics, furniture), they depreciate, making the opportunity cost analysis appropriate.

For small regular spending habits it can be eye-opening — daily coffee at $5 is $1,825/year, which at 4% SWR removes $45,625 from your retirement portfolio. But don't over-optimize small purchases at the expense of larger levers like income, savings rate, and investment allocation.

The true retirement cost of a $30,000 car is far more than $30,000. At 5% real return over 20 years, $30,000 grows to approximately $80,000 — that is the opportunity cost. At a 4% withdrawal rate, $30,000 also represents $1,200/year in annual retirement income you permanently forfeit. The calculator above shows your exact FIRE delay and opportunity cost based on your specific situation.

Every dollar spent reduces your net worth and therefore takes longer to replace through savings. A $20,000 purchase delays FIRE by roughly 4–12 months depending on your savings rate and current net worth. A $50,000 purchase can delay FIRE by 1–3 years. The delay is not linear — the same purchase delays someone with $50,000 net worth far more than someone with $500,000, because a larger portfolio generates more growth to offset the loss.

From a pure FIRE perspective, buying a reliable used car with cash is almost always optimal — it eliminates monthly payments, depreciation is absorbed by the previous owner, and insurance is lower. A new car typically loses 20–30% of its value in the first year. If you finance a new car at $500/month, that is $6,000/year not compounding toward your FIRE number — equivalent to removing roughly $150,000 from your retirement portfolio at a 4% SWR.

The highest-impact daily habits are those that run on autopilot: automatic investment contributions, maintaining a low fixed-cost lifestyle, and avoiding lifestyle inflation as income grows. Individual small purchases (coffee, lunch) have limited direct impact compared to large recurring expenses (housing, car payments, subscriptions). The calculator is most powerful for evaluating major purchases — for small purchases, focus your optimisation energy on the bigger fixed costs first.