Coast FIRE spreadsheet
The same math as our calculator, in a file you can keep, change and pick apart. It works in Excel, Google Sheets and Numbers, and there's nothing to sign up for.
mycoastfire-coast-fire-spreadsheet.xlsx
Three tabs: calculator, year-by-year table, and targets by age.
What's inside
The first tab is the calculator. You fill in eight green cells: your age, the age you want to retire, yearly spending in retirement, what you have invested, what you add each month, and your return, inflation and withdrawal rate. It works out your real return, your FIRE number, your Coast FIRE number and how far you are from it. With the default numbers, the Coast FIRE number comes out to $395,332, exactly what the online calculator shows.
The second tab runs your balance forward one year at a time, stops your contributions the year you cross the Coast FIRE line, and marks that year. The third tab is a grid of Coast FIRE numbers for ages 20 to 60 at four spending levels, using whatever assumptions you entered.
How to open it
In Excel or Numbers, just open the file. For Google Sheets, upload it to Google Drive and open it with Sheets, or go to File, then Import, in a blank sheet. The formulas carry over, including the named cells that keep them readable.
The formulas
If you'd rather build your own, these are the three that matter. Cell names match the spreadsheet.
FIRE number = Spending / WithdrawalRate
Real return = (1 + Return) / (1 + Inflation) - 1
Coast FIRE number = FIRE number / (1 + Real return) ^ (RetirementAge - CurrentAge)The Coast FIRE number guide walks through each step with an example, and the methodology page explains the default assumptions.
Spreadsheet or calculator?
The spreadsheet is better if you want to track your own progress over time or change the model, say by adding a raise every year or a one-off windfall. The calculator is quicker for trying scenarios, draws the chart for you, and has versions for Social Security, couples and market ups and downs. Plenty of people use both.
Questions people ask
Is the spreadsheet really free?
Yes. There's no email sign-up and no paid version. Download it, change the green cells, and keep it as long as you like.
Why does the spreadsheet show a different Coast FIRE age than the website?
The spreadsheet adds contributions once a year, which keeps the formulas simple. The online calculator works month by month, so it can land a year earlier. The Coast FIRE number itself is identical.
Can I add Social Security or a second person?
The simplest way is to adjust the inputs: subtract expected Social Security from yearly spending, or add both partners' balances and contributions together. The online Social Security and couples calculators do this for you.