The years between starting to save and hitting your FIRE number feel endless. This chart shows you exactly how compound interest bends the curve — and what happens when you layer in extra monthly savings (any amount you choose).
* Based on 7% real (inflation-adjusted) returns. FIRE number = annual spending × 25 (4% SWR). Coast FIRE number = FIRE number ÷ (1.07)^(65−current age). Source: Trinity Study (1998), Bengen (1994).
In the early years of saving, your contributions dominate your portfolio growth. If you save $2,000/month and your portfolio earns 7%, the returns on a $50,000 portfolio are only $3,500/year — less than 2 months of contributions. Progress feels linear. It feels like work.
But as the portfolio grows, the math inverts. At $300,000, 7% returns generate $21,000/year — almost a full year of contributions. At $600,000, returns match everything you're putting in. Above that, the portfolio grows faster than you can contribute. That's the bend in the curve — and it arrives faster than it feels.
An extra $1,000/month invested at 30 is worth far more than the same amount at 45 — not because of the contribution itself, but because of compounding time. Money added at 30 has decades to grow before a typical retirement age. The same amount at 45 has fewer years.
Use the extra monthly savings slider above to compare your baseline plan with a higher contribution (side-by-side curves). The earlier you are, the more timeline compression you tend to see. This is why the FIRE community's core message — savings rate matters more than income — is mathematically correct.
Source: compound interest formula A = P(1+r)^n + PMT×[((1+r)^n−1)/r]. Real return 7% per annum. All projections are illustrative — actual returns vary.