A developer built a financial planning tool that simulates money day-by-day to age 112 in today's dollars, answering how long you need to work at a high salary before stopping, coasting, or retiring. Built in a conversation with Claude, it models wages, taxes, expenses, and investments with a safety factor.

The tool solves for three goals: retire to $0, coast until 60, and flat from 100. It outputs stop ages, portfolio values, income-plan tables, and terminal charts.

What-if tables show savings impact, while moving-city plans switch expenses and taxes at a given age. Grid sweeps cover cities, income ladders, partner incomes, and account types including 401(k), Roth, and 523.

Plans are plain Python, so Claude Code can generate custom plans from plain-English descriptions. Personal numbers stay in a gitignored custom_plans/ folder.