Field in which the rule of 70 gives a rough idea of how long an investment takes to double in value (8,8)

I believe the answer is:
compound interest
(Other definitions for compound interest that I've seen before include "What may be added to an account" , "It may be paid on an account" .)
I've seen this clue in The Sunday Times and The Times.
Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free.
Check out my app
or
learn more
about the Crossword Genius project.