Leaving a job to start a business (run these 6 numbers first)

Most pages on this question ask about your character. Leaving a job to start a business comes down to 6 numbers, including the 1 your payslip never shows you.
Starting a business at 50 (10 things that changed since you were 35)

Starting a business at 50 puts you past the average founder age. Here are 10 things that changed in your situation since 35, and 2 that get harder.
How to start a business while working full time (in a job you hate)

Most advice measures how much you dislike the job. These 10 items measure what is actually holding you there, plus the 4 things worth doing this month while you are still drawing a salary.
10 signs it’s time to quit your job and work for yourself

Most lists measure how much you dislike the job. These 10 signs measure whether customers will pay you once you leave, plus the 4 numbers to look up before you give notice.