firenum vs ProjectionLab: An Honest Head-to-Head

Mikulas  · August 2026 · ~7 min read

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 lets you share snapshot URLs and swap between them, which is a workaround, not a feature.
• 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 recovery path, job loss, expense spike, inflation surge, lower returns, earlier retirement.

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.
• 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.