Methodology & data sources
Transparency is the core of our E-E-A-T. This page documents the IRS figures we cite, how often they refresh, and the exact formula behind every calculator. All results are estimates for general information, not financial advice.
Data sources
| Source | Refresh cadence | License |
|---|---|---|
| IRS Notice 2025-67 (2026 retirement plan limits) | annual | Public domain (U.S. Government work) |
Announced November 2025; effective for the 2026 tax year. Data as of the 2026 tax year.
The formulas
| Calculator | Core formula |
|---|---|
| FIRE number | FIRE number = annual spending ÷ withdrawal rate (e.g. spending × 25 at 4%). Years-to-FI iterates current savings × (1 + return) + contribution until it reaches the target. |
| Coast FIRE | Coast target today = FIRE number ÷ (1 + return)^years to retirement. You are coasting when current savings exceed that. |
| Compound interest | FV = P(1 + r)^n + PMT × [((1 + r)^n − 1) ÷ r], compounded monthly. |
| 401(k) match | Employer match = salary × min(your %, match cap) × match rate. We compare it to the maximum match to show any amount left on the table. |
| Roth vs Traditional | Roth = contribution × (1 − tax now) × (1 + r)^n. Traditional = contribution × (1 + r)^n × (1 − tax later). Equal tax rates break even. |
| 4% rule / drawdown | Year-one income = portfolio × withdrawal rate; each year the balance is (balance − spending) × (1 + return) and spending grows with inflation. |
2026 IRS limits we use
| Limit | 2026 amount |
|---|---|
| 401(k) elective deferral | $24,500 |
| 401(k) catch-up (50+) | $8,000 |
| 401(k) catch-up (60–63) | $11,250 |
| Combined employee + employer | $72,000 |
| IRA contribution | $7,500 |
| IRA catch-up (50+) | $1,100 |
Assumptions & limitations
Calculators run in your browser; we do not store your inputs. Returns are assumed constant and do not model market volatility, sequence-of-returns risk, fees or taxes on growth unless stated. The 4% rule is a historical guideline, not a guarantee. Figures may lag changes to IRS limits or contain errors — always verify against the primary source before relying on them. See our disclaimer.
Last updated: 2026-06-14