People talk about "making the leap" in really vague terms. I did it last year and wish someone had walked me through the numbers more concretely before I made the decision. Here's what actually mattered.
The baseline calculation everyone gets wrong: You don't need your side project to replace your salary. You need it to replace your total compensation minus what you save in taxes by being self-employed, plus what you'll spend on benefits you previously got for free.
For me in 2025, that math looked like: Old salary + bonus: $185k Health insurance I was getting free: ~$8k/year (employer was paying ~$22k total) 401k match I was losing: ~$6k Self-employment tax vs W2 (SE tax is 15.3% on net, but half is deductible): roughly $8k worse for me Total I actually needed to replace: something closer to $200k equivalent if I wanted to maintain the same position
The runway question: Most advice says "6 months of expenses." I think that's too short for a product business because you don't know when it starts working. I went with 18 months of personal expenses in savings before I quit. That felt tight by month 14 but I made it.
The "ramen profitable" milestone: This is the one I actually aimed for before quitting: project revenue covering my minimum monthly expenses (rent, food, health insurance). Not profit. Not salary replacement. Just minimum viable survival. I hit that at around $3,800/month in revenue before I gave notice.
What I underestimated: Quarterly estimated taxes. You pay them four times a year now, and if you forget or underpay you get penalties. The cost of losing accountability. I'm more productive than I expected but the first 3 months had more wasted days than any year of full-time work. Health insurance open enrollment timing. If you quit in March you might not be able to get good coverage until November without paying a lot for a marketplace plan.
I don't regret it. The project is doing okay. But I'd have stayed 4 more months if I'd done this math correctly the first time.