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FireFlyy: FIRE Calculator for All 5 Milestones
Open appKnow your financial independence number — FireFlyy calculates every FIRE milestone (LeanFIRE, CoastFIRE, BaristaFIRE, FIRE, FatFIRE) from your actual household, spending, and savings data. Free and educational.
Problem Statement
FIRE calculators online are oversimplified — most compute only a single number and don't distinguish between the five recognized FIRE variants. Users with different income, spending, and risk profiles get one-size-fits-all results that don't reflect their real situation.
Solution
FireFlyy computes all five FIRE milestones simultaneously — LeanFIRE, CoastFIRE, BaristaFIRE, FIRE, and FatFIRE — from actual household income, monthly spend, and savings data. Users see exactly where they stand on each path and what it would take to reach each milestone.
Our Approach
We modeled each of the five FIRE variants as a distinct target expense multiple and savings-rate assumption, then ran all five calculations off a single shared intake of household income, monthly spend, and current savings so users didn't have to re-enter their data five times. The results view plots progress toward every milestone at once, so a user can see, for example, that they've already hit BaristaFIRE while CoastFIRE and full FIRE are still years out.
Key Features
- Single data intake that powers all five FIRE milestone calculations at once
- Side-by-side progress view comparing LeanFIRE through FatFIRE on one timeline
- Free, education-first framing with no account or paywall required to see results
Results
FireFlyy replaces five separate single-purpose calculators with one workflow, and the multi-milestone comparison view is the most-cited feature in user feedback — it reframes FIRE progress as a spectrum rather than a single pass/fail number, which is closer to how most people actually plan.
Challenges
The five FIRE variants use materially different assumptions about spend flexibility and side income, so the main engineering challenge was keeping the calculations independently correct while sharing one intake form. We unit-tested each milestone formula against published FIRE-community reference calculations to validate accuracy.
Lessons Learned
Presenting multiple related financial outcomes side-by-side, instead of picking one 'primary' number, better matches how users actually think about long-range goals with uncertain timelines.
Tech Stack
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