The FIRE & Coast FIRE Calculator Pack — Seven linked calculators, every formula checked by recalculation

Seven calculators for financial independence, in today's dollars. Start with sheet 1 for your number and sheet 4 for the Coast FIRE figure; sheet 7 does both for a couple. The withdrawal rate is always yours to choose -- sheet 5 shows what one point either way costs, which on the worked example is $400,000 of target in one direction. Every formula was recalculated and checked against an independent implementation before this shipped; see the Verification sheet.

What is in it

7 calculators, one per sheet. Overwrite the blue cells with your own numbers and everything else follows — nothing is locked, there are no macros, and it opens in Excel, Numbers, LibreOffice and Google Sheets.

• FIRE number — How much do you need invested to live on the withdrawals?
• Real versus nominal return — What does your return look like once inflation is taken out?
• Years to FI — At your savings rate, how many years until you reach the number?
• Coast FIRE — How much do you need today to stop saving and still get there?
• Withdrawal rate sensitivity — How much does one point of withdrawal rate move the target?
• What a spending cut is worth — What is each $100 a month of spending cut worth in years?
• Couples FIRE and Coast — Two incomes, one household: what is the number, and when?

Every formula was checked

This pack contains 51 formulas. Before it was published, every one of them was recalculated by a spreadsheet engine and compared against an independent implementation of the same arithmetic written in Python. All 51 agreed to within a cent, and the workbook carries a Verification sheet saying so.

That is an unusual thing to be able to claim about a spreadsheet, and it is the main reason to buy this one rather than download a free template. A formula that looks right and is wrong is worse than no formula at all, because you will act on it.

What each calculator assumes

There is a sheet listing this, because a calculator that hides its assumptions is just a number generator:

• The withdrawal rate is yours to choose. This pack does not say which rate will last; it shows what each choice costs.
• A steady return and steady inflation every year. Real markets are neither; the order of good and bad years matters and no average shows it.
• Contributions are made at the end of each year and stay level in today's dollars (they rise with inflation in cash terms).
• After reaching the Coast number you still cover your spending from work until the stop age, but add nothing to the investments.
• Same real return and contributions at every rate tested.
• The money cut from spending is invested, and the lower spending lasts into retirement.
• Both incomes continue until FI and all savings are pooled. Accounts in one name, taxes and pension timing are not modeled.

What this is not

Not financial, tax or legal advice, and not a recommendation to buy, sell, borrow or sign anything. These are calculators: they show what a choice costs, not which choice is right for you. Where a published rate or threshold is used it is the one current when the pack was built — those change, the arithmetic does not.

Honest about the format

One .xlsx workbook, 7 calculator sheets plus Start Here, Assumptions and Verification. Not a PDF, not a physical product, not a Notion template. Available immediately after purchase; nothing ships.

Refunds

If this isn't what you expected, email me within 30 days and I'll refund you in full — no need to explain. Because it's an instant download I can't take the file back, so I'd rather you just had your money back.