Here's myRetirement Early Calculator. That will help perform a simplified but complete back-of-the-envelope Financialy Independence Retire Early calculation to see if and when you can implement your FIRE strategies. Naturally any calculator has limitations related to your projections as well as changing TAX and ECONOMIC conditions over time.

This is open source, and for any other folks interested out there I have linked this source code on GitHub, if you wish to modify the calculator orrequest a feature or just mess with this calculator.