The Compound Planner - interactive savings and investment calculator

A single-file interactive calculator that shows what a starting amount plus a monthly contribution actually becomes over one to forty years.

What it does:

- Three rate scenarios at once - low, middle and high - so you read a range instead of one false-precision number - Annual step-up on the contribution, because most people can raise it a little each year and the difference is large - A live chart with your contributed capital as a shaded floor, so the gap between line and floor is the growth - The crossover month: the first month growth exceeds everything you have put in - Full month-by-month table with copy-to-spreadsheet and print-to-PDF - Start or end of month contribution timing - Any currency label, dark and light mode, works offline, sends nothing anywhere

The maths is stated plainly in the guide, including what it deliberately does not model: tax, fees, inflation and withdrawals. It is a projection tool, not financial advice.