FIRE and retirement calculator

Age, what you have, what you add, real returns, the spending you want and the withdrawal rate that sets the target. You get the year and age you reach it, the balance then, and whether it lasts to the age you plan to, in today's money. Same logic as the Bindler workbook, verified against it.

Where you are
What you want
Everything is in today's money: enter real returns (a 7% nominal return with 3% inflation is about 4% real). Contributions arrive through the year, so growth is on the opening balance plus half the contribution.
The workbook: every year of accumulation and drawdown, in your own fileRetirement and FIRE Planner, $12: Inputs, Summary, seventy years of accumulation, seventy-five of drawdown, and a Guide. Both schedules verified through a formula engine before listing.
See the workbook

Method: target = spending over the withdrawal rate. Each saving year: contribution (growing at the real rate you set; zero once the target is reached), growth on the opening balance plus half the contribution, closing balance. From the year the target is reached: spending out at the start of each year, real return on the rest, to the plan age. A single average return; real markets are not, and sequence-of-returns risk, tax and pensions are outside this page. Same logic as the Bindler workbook. Arithmetic on your assumptions, not financial advice.