Honest comparison

The FIRE Calculator Landscape, Honestly

Written for the FIRE-knowledgeable person everyone else asks. What each tool genuinely does well, what each one costs or omits, and the recommendation that won't get you blamed.

9 min readLast reviewed July 2026

Written by Luke Newton — software & financial services background, not a registered investment advisor. About the builder →

Who this is for

If you're already using ProjectionLab, cFIREsim, or your own spreadsheet — this isn't trying to compete on depth. It's the recommendation for the people in your life who ask “what calculator should I use?” — and for standard-FIRE planners who don't need 12 asset classes modeled to answer “am I on track?”

The current default recommendation is broken

When someone asks “what calculator should I use,” the practical options today are:

Option	The honest problem
Empower / Personal Capital	Free, but it's a wealth-management lead-generation tool. Your friend gets advisor calls within weeks of signing up.
Vanguard / Fidelity calculators	Free, but too thin to model anything specific. No bridge years, Roth conversions, or sequence-of-returns risk.
Boldin / ProjectionLab	Substantively good, but $129–$144/year and 30 minutes to 2 hours of setup. The friend probably won't actually use them.
FIRECalc / cFIREsim	Free, open-source, rigorous history — and model no taxes at all, which for an early retiree is a large omission.
A 4% rule worksheet	Useless for a real answer. Here's the honest treatment of why.

So the FIRE-knowledgeable recommender either gives a non-answer (“just save more”), points at Empower and accepts the lead-gen risk, or hands over their own ProjectionLab login — which isn't going to happen.

$79 one-time. Real Monte Carlo. No data collection. No upsell funnel. The friend gets a meaningful answer in five minutes — and the recommender doesn't get blamed for sending them into a sales pitch.

A note from the builder

I built this because at 49, I was tired of two options: oversimplified calculators (the 4% rule doesn't tell you much) and overcomplicated subscription tools (I didn't want to model 12 asset classes manually to ask a simple question).

Most retirement-tool conversations among FIRE-knowledgeable people are about which depth-tool to use — Boldin or ProjectionLab or build-your-own. Those are good questions. But the people in your life asking what to use aren't asking that. They're asking: “is there something between a free calculator that doesn't say anything and a $144/year tool I'll never set up?”

This is built for that gap. Real Monte Carlo math, real Social Security modeling, real tax-optimal withdrawal sequencing. $79 once, no subscription, no account, no hidden funnel. Sound enough that you can point a friend at it without worrying they'll be misled or upsold — and honestly, sound enough that for a standard-FIRE plan, you might find yourself using it too.

— Luke

What it models that matters for FIRE

The math is the same whether you're targeting 65 or 50 — what changes is which features matter most:

1,000-scenario Monte CarloReal probability of plan survival, not a single-point estimate. How it works, honestly.

Historical back-testingReplay your plan against every market sequence from 1928 onward, or by named stress era — the Bengen / Trinity methodology, next to Monte Carlo.

Actuarially correct Social SecurityProper FRA adjustments, claiming-age modeling, spousal and survivor benefits.

Tax-optimal withdrawal orderingTaxable, then tax-deferred, then Roth — modeled inside every simulation.

Phase-based spendingGo-go / slow-go / no-go boundaries you define; spending that tapers with age.

Coast FIRESet a stop-contributing age; balances compound through to retirement.

Guyton-Klinger guardrailsDynamic spending that cuts in bad markets and bumps in good ones — opt-in, honestly capped.

Roth conversion sweet spotFinds bracket headroom in low-income post-retirement years.

Gain harvesting (0% LTCG)Resets brokerage cost basis in bridge years at zero federal tax; pairs with conversions.

Bridge reserve modelingEarmark cash, home sale, or inheritance to fund the years before Social Security.

Healthcare bridge + ACA subsidiesExplicit pre-Medicare cost modeling with the subsidy cliff — the early-retirement expense most calculators ignore.

Sequence-of-returns stressThe most important risk most free calculators don't model.

Backdoor & Mega Backdoor RothModeled correctly — the high-earner staple, often ignored.

SS Benefit Confidence sliderModel Social Security at 70–100% of projected — the honest hedge every FIRE planner wants against the 2033 trust-fund question.

Future one-time expensesPlan-aware lump outflows at specific ages — college help, gap-year travel, a roof.

AI AdvisorInterrogate scenarios conversationally — “if I convert $50k/yr from 65–70, what happens to my IRMAA exposure?”

What this isn't

Honest about limits — important if you're vouching for it:

Not a full craft-planning tool like ProjectionLab or cFIREsim. If your friend turns out to be a craft planner, send them there — here's our honest comparison.
No Vanguard dynamic spending or Kitces ratcheting (Guyton-Klinger guardrails are supported).
Single return-rate assumption (separate pre- and post-retirement rates) — no per-asset-class allocation modeling.

How to recommend it well

Tell them it takes five minutes. That's actually true, and the friction sink is what kills most tool recommendations.
Tell them no account is required. The differentiator from Empower they won't realize matters until you name it.
Tell them $79 is the upgrade, not the entry. The free version runs the full Monte Carlo and gives a real answer.
Set the success-rate target appropriately. 85%+ for a traditional retirement; 95%+ if they're targeting 50 or earlier.
Point them at the SS Benefit Confidence slider if they're decades from claiming.

Every formula, assumption, and source — the cohort tables, the SSA worker profiles, the IRMAA thresholds, the Monte Carlo distribution, the tax brackets — is published in the methodology, and the testing regimen behind it is public in the trust framework. Vet it before you recommend it.

Common questions

What's the best free FIRE calculator?

For pure historical back-testing, FIRECalc and cFIREsim are excellent and open-source — the most rigorous free replay-history tools available, though they model no taxes. For full-plan modeling with taxes, Social Security, and Monte Carlo, our free tier runs the complete engine with no account. They answer different questions; a careful FIRE plan benefits from both a historical view and a simulated one.

FIRECalc vs cFIREsim — what's the difference?

Same core method — replay your plan against every rolling historical market sequence since 1871 — with different interfaces. cFIREsim is the more actively maintained open-source descendant with more configuration options (variable spending, allocation changes). Both are free, both are legitimate, and both deliberately ignore taxes, which is the biggest gap to know about.

Is the 4% rule enough for FIRE planning?

As a napkin estimate, it's a fine starting point. As a plan, no — it was built and tested on 30-year retirements, and a FIRE-length horizon of 40–50+ years faces meaningfully more sequence risk. Research on longer horizons generally lands nearer 3.0–3.5%. We wrote a full honest treatment of where the rule came from and when it breaks.

Vet it yourself in five minutes — full Monte Carlo, real taxes, historical back-test, no account. Then decide whether it earns the recommendation.

Try it free →