Guwahati, Nov. 5 -- Mutual fund calculators look alike on the screen, but they answer very different questions. A lumpsum calculator shows how a one-time investment may grow, while an SWP calculator shows how a pool of money may last when you withdraw from it. Knowing which question you are asking tells you which tool to open. This article sets out what each one does, how they differ, and how they can work together.

A lump sum calculator tells you what a single investment made today could be worth later. All you need is the amount you are putting in, the return you expect each year, and how long you plan to stay invested.

Behind the scenes, it uses a simple compound growth formula: Future value = P x (1 + r)^n. P is the amount you put i...