About FI Plan Lab
Free FIRE calculators built by a blockchain and financial systems researcher at the University of Verona. Methodology, mission, and contact.
Who Built This
Muhammad Bin Saif is a PhD researcher in Computer Science at the University of Verona, Italy, where his work focuses on blockchain systems, zero-knowledge proofs, and decentralized financial architectures. He has published in IEEE ICBC, IEEE BCCA, and Future Internet (MDPI), and holds a fully-funded PNRR scholarship from the Italian Ministry of University and Research.
The connection between that research and a FIRE calculator suite is less strange than it sounds. A large share of his published work deals with financial data systems — verifiable compliance logic, tamper-proof transaction records, cost modeling for decentralized storage. That work demands the same thing good retirement math demands: knowing exactly what a formula guarantees, where it breaks, and what happens when the inputs are wrong.
Most FIRE calculators he found online were either too simple to be honest or too opaque to trust. FI Plan Lab is his attempt at something in between — tools that use real formulas without hiding the uncertainty those formulas carry.
Why It Exists
FIRE planning is often explained either too casually or too precisely to be useful. The casual version tells you to multiply your expenses by 25 and call it a day. The precise version buries you in Monte Carlo percentiles until you lose track of what you were actually trying to decide.
This site occupies the middle ground. The calculators use monthly compounding, not the rough annual shortcuts that inflate timeline estimates. They model tax drag, Social Security bridge years, and inflation-adjusted purchasing power — variables that most free tools ignore and that have a real effect on when you can actually stop working.
Every calculation runs locally in your browser. No data leaves your device.
Methodology
The accumulation phase uses compound interest iterated monthly. The formula at the core is straightforward: target portfolio = annual retirement spending ÷ withdrawal rate. From there, the tool iterates month by month until the portfolio crosses the threshold. Monthly compounding matters because real contributions and real returns arrive throughout the year, not in a single annual lump.
The Monte Carlo stress test runs 1,000 simulations with randomized annual returns drawn from a distribution centered on your expected real return. The output is not a single number but a survival probability — the share of simulations in which the portfolio survives to the end of the retirement horizon.
The primary research foundations are the Trinity Study (Cooley, Hubbard, and Walz, 1998), the safe withdrawal rate work of William Bengen (1994), and long-run equity return data from NYU Stern. For deeper reading, start with the 4% rule article and the guide to calculating your FIRE number.
A Note on Limitations
These tools are for planning, not prediction. A model that assumes 7% real returns will give you a different answer in a decade than it gives you today. Sequence-of-returns risk — the possibility that a bad market run happens early in retirement rather than late — is the thing most deterministic projections cannot show. That is precisely why this site pairs the main calculator with a Monte Carlo test.
Use the results as a framework for decisions, not a guarantee of outcomes.
Contact
Questions, corrections, or ideas for new calculators: contact@fiplanlab.com
This site does not constitute financial advice. The tools are for educational purposes.
Contact
Use this form for feedback, partnerships, or calculator questions.