Enter the price of a bottle and how many you buy a week to see the yearly and ten-year total.
A refillable bottle is a near-free swap; the invested figure shows what the difference could become.
How it's worked out
Yearly cost = price × times per week × 52. The “if invested” figures assume you put the same amount in each year and it grows at the rate you set (default 7%) — an ordinary annuity. They're estimates to show scale, not guaranteed returns.