firenum vs ProjectionLab: An Honest Head-to-Head

Full disclosure at maximum strength: I build firenum. A comparison page written by one of the competitors is either the least trustworthy page on the internet or the most, depending on one thing: whether it names the places its own product loses. This one does, specifically and first.

Where ProjectionLab Beats firenum

• Tax modeling. ProjectionLab estimates US federal and state taxes year by year. firenum doesn't model taxes at all; you approximate them as expenses. If your plan depends on tax strategy, ProjectionLab is the right tool and this comparison ends here for you.
• Roth conversion planning. Conversion ladders with year-by-year tax consequences. firenum has nothing comparable.
• Scenario comparison. Premium's side-by-side compare mode (retire at 45 vs 50, with all charts duplicated) is the best in the category. firenum keeps up to 5 named plans in your browser and compares them in one table (when each retires, whether the money lasts on average returns, its Monte Carlo and historical backtest counts, net worth at retirement), with no side-by-side charts.
• Milestone storytelling. ProjectionLab's life-event timeline and progress views are more polished and more motivating.

Where firenum Beats ProjectionLab

• Price: $0 with persistence. ProjectionLab's $0 tier can't save your plan; saved plans cost $129/year. firenum saves everything in your browser's localStorage at no cost, forever, because there's no server to pay for.
• Privacy architecture. firenum has no accounts and no database. Your plan physically cannot leak from a server that doesn't exist. ProjectionLab requires an account and stores plans in the cloud (with a good privacy reputation, to be fair).
• Multi-currency. firenum supports 9 currencies with real locale formatting (lakh/crore for INR, 万 for JPY). ProjectionLab's multi-currency request has been its most-voted open issue since November 2021.
• Cash-flow visualization. firenum draws a full Sankey diagram of where every dollar flows in any projection year, plus a Trinity-style portfolio survival heatmap across withdrawal rates.
• Stress testing. Six one-click scenarios: market crash with slower growth after it, job loss, spending spike, inflation surge, lower returns, retiring earlier or later.

Feature by Feature

The Simulation Engines Are Closer Than You'd Think

Both tools run drift-corrected Monte Carlo and both backtest against real historical returns. On the math that decides whether your plan survives, the two produce comparable answers; firenum documents its full methodology with derivations if you want to check the work. The differences that matter are around the engine: taxes on their side, privacy and currency handling on ours.

The Honest Answer: Many People Should Use Both

These tools charge differently because they're built differently. ProjectionLab pays a team through subscriptions and gives you tax-aware depth in return. firenum costs nothing to run per user (static files, your browser does the math) and gives you privacy and breadth in return. A workflow I genuinely recommend:

• Do your everyday planning, check-ins, and stress tests in firenum: private, instant, saved locally. For a one-minute answer, the free FIRE calculator gives your retirement year.
• When a decision has real tax consequences (a Roth ladder, a big taxable sale, ACA subsidy planning), model that decision in ProjectionLab : the $0 tier will show you whether the Premium depth is worth it for your case.

Verdict

If you need US tax modeling, pick ProjectionLab and don't look back; our full ProjectionLab review rates it 4.5/5. If you want private, multi-currency planning with everything saved and nothing paid, pick firenum. If you're serious about early retirement, the combined cost of using both is $0 to $129 a year, which is a rounding error against the decisions they'll improve.