Your numbers
Use after-tax (take-home) income. Savings = anything you do not spend: 401k contributions, IRA, brokerage, extra mortgage principal.
How this is calculated
Savings rate = monthly savings / monthly take-home income x 100. Annual spend = (income - savings) x 12. FI number = annual spend x 25 (the 4% rule). Years to FI is computed by iterating: each year the balance compounds at the real-return rate and adds your annual contribution until it reaches the FI number. If current balance already covers FI, the answer is "you are there."