I'm not sure if this has been talked about somewhere else, I couldn't find anything.

I was just crunching some hypothetical numbers after reading a post on

http://earlyretirementextreme.com where he talks about needing your monthly cost of living x 300 to live off the interest. The question I have though, is there anyway to do an simple calculation to figure out this number if we DON'T want to retire, but just want to work less.

So here's my hypothetical projections:

If we can live on 4,000 per month.

Then we need 4,000x300= 1,200,000

@3,000 per month savings we have 1.2m in 17 years

@5,000 per month we have 1.2m in 12 years

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If we can live on 3,800 per month

Then we need 3,800x300 = 1.14m

@3,000 we have 1.15 16 years

@5,000 we have 1.4 12 years

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$3,000/m cost of living

@3,000 we have 900k in 14 years

@5,000 we have 900k in 10 years

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So cool, if we can get our cost of living down to 3k per month and save 5k per month, then we're FIRE in 10 years! But is there a simple way to work into this calculation to see what happens if we can have working income of say 2k or 4k per month after that 10 year point?