FireMathLab

Guides: FIRE, debt and saving, explained properly

Each guide answers one question with worked numbers, then hands you the calculator that produced them.

42 guides · page 2 of 5

savings18 August 20265 min read

How to use the savings goal calculator

Turning a target and a deadline into a monthly figure, deciding whether to hold the money in cash, and what to do when the number is too big.

fire18 August 20265 min read

How to pick a safe withdrawal rate

Where the 4% rule came from, why it may not travel to the UK, and how to choose the percentage your own plan should use.

fire18 August 20265 min read

How to use the retirement crash test

What a 35% fall in your first year of retirement does to a plan, why timing matters more than size, and the fixes that actually work.

fire18 August 20265 min read

How to use the retirement backtest

Running your plan against real historical sequences, why 1966 matters more than 1929, and what a failed cohort actually tells you.

property18 August 20265 min read

How to use the rent vs buy calculator

Setting the purchase and rental sides fairly, what the break-even year actually means, and handling purchase tax outside the UK.

fire18 August 20266 min read

How to use the pension bridge calculator

Funding the years between stopping work and reaching your pension, sizing the bridge pot, and splitting contributions between ISA and pension.

budgeting18 August 20265 min read

How to use the payday allocator

Splitting your pay the day it lands, deciding the order money should leave, and why allocating beats budgeting for most people.

networth18 August 20265 min read

How to use the net worth tracker

What counts as an asset, how monthly check-ins work, reading the rings and trend charts, and why the direction matters more than the number.

property18 August 20265 min read

How to use mortgage overpayment

What a regular overpayment does to your term and interest, the 10% annual limit, and when overpaying beats investing the same money.

fire18 August 20266 min read

How to read a Monte Carlo retirement run

Why one average return hides the real risk, what a success rate does and does not promise, and which number to aim for.