Build a few "what if" plans, save them, and see them compared on one chart. Change one thing at a time — a bit more each month, a few more years, a calmer return — and watch what it does. Your plans are kept on this device for next time.
These lines are deliberately smooth — that is the point, and the limitation. Every plan grows at a fixed return with no bumps, so the only thing separating two lines is the assumptions you changed. That makes a like-for-like comparison honest and easy to read.
It is not what any one plan will actually do. Real returns arrive unevenly, and a single smooth line hides how wide the real spread is. For the honest range of outcomes on one plan — including how often it ends badly — use What’s Possible. Use this tool to compare, that one to judge.
A smooth line is a useful way to compare assumptions and a poor way to predict an outcome.
That is the arithmetic. The thinking behind it is thirteen short lessons on the things that matter more than any single strategy.