How Much Part-Time Income Do You Need to Coast FIRE? The Simple Formula

Published October 16, 2026

How much part-time income do you need to coast FIRE? Subtract what your savings can already sustain from what you spend. That gap is the number your coasting job has to cover, and the answer usually surprises people in both directions.

Coast FIRE has a marketing problem. It gets sold as "never save again," and then the first question anyone asks is the one the slogan dodges: okay, but how much do I have to earn? I do not love the slogan either. It makes coasting sound like quitting, when it is really a math problem about who pays this year's bills while your portfolio does the long compounding work untouched.

The formula

Part-time income needed = annual expenses - (current savings x safe withdrawal rate)

That is the whole thing. Your savings cover the second term on their own; your work covers the rest. Use 4% as the withdrawal rate for the standard version, 3 to 3.5% if you want a conservative read on a 40-plus year timeline.

Worked example one: $200k saved, $45k expenses

Your savings sustain $200,000 x 4% = $8,000 a year. Part-time income needed: $45,000 - $8,000 = $37,000 a year, about $3,083 a month.

In hourly terms: at $25 an hour, that is roughly 29 hours a week. At $20 an hour, about 36. The part-time label starts looking optimistic at this savings level, which is exactly the point of doing the math before you quit the good job.

Worked example two: $300k saved, $36k expenses

Your savings sustain $300,000 x 4% = $12,000 a year. Part-time income needed: $36,000 - $12,000 = $24,000 a year, $2,000 a month.

At $25 an hour, that is about 15 hours a week. Two solid days. This is the version of coast FIRE the brochures describe, and it only exists because the savings are doing half the work.

Healthcare changes the answer more than anything else

Both examples above hide the line item that breaks budgets: insurance before Medicare. One FIRE calculator's walkthrough puts it plainly: $35,000 in living expenses plus $8,000 in ACA healthcare means $43,000 of income needed, and a $20-an-hour job at 25 hours a week covers only $26,000 of it. That leaves a $17,000 gap people discover in year one.

So run the formula with your full insurance cost inside annual expenses, not next to them. An $8,000 ACA premium is $667 a month of part-time income before you have spent a dollar on food.

The part nobody prices honestly

Here is the question the formula cannot answer: does the part-time work have to be work you like? The entire coast FIRE community assumes you will downshift into something pleasant, a bookstore, a national park gig, consulting a few hours a week. Nobody models the scenario where the pleasant jobs pay $16 an hour and the boring ones pay $40. I have no formula for that. But I would rather you notice the assumption before year three, when the pleasant job still pays $16 an hour and the math says it always will.

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Frequently asked questions

How much part-time income do you need to coast FIRE?

Part-time income needed = annual expenses minus (current savings x safe withdrawal rate). With $200,000 saved and $45,000 in annual expenses, your savings cover about $8,000 a year at 4%, so you need roughly $37,000 a year from part-time work, about $3,083 a month.

Does the part-time job need to provide health insurance?

It does not have to, but healthcare is usually the biggest gap in the budget before Medicare at 65. Include your full ACA premium in your annual expenses before running the formula. An $8,000 ACA plan adds about $667 a month to the part-time income you need.

Can side hustle or freelance income count as coast FIRE income?

Yes, as long as it reliably covers the gap every year. The danger with irregular income is the lean years. Use a conservative average of what you actually earned over the last two or three years, not your best year.

Does Social Security reduce the part-time income I need?

Yes. Social Security shrinks your retirement target, which shrinks your Coast FIRE number and the pressure on your coasting years. With $50,000 in expenses and $20,000 in expected Social Security, your gap is $30,000, which cuts the full FIRE target from $1.25 million to $750,000 at a 4% withdrawal rate.