# E (Compound Interest Definition)

## Colorized Definition

## Plain English

**What is e?**A constant (2.718...) representing*continuous unit growth*: the unit quantity (1.0), continuously growing the unit rate (100%), for unit time (1 period).**Why's e special?**All circles are the unit circle, scaled up. All continuously growing systems are e^{rt}, scaled to some rate and time.**When should I use e?**Use e^{rt} for things that change constantly (radioactive decay, populations). For growth based on discrete intervals (interest payments, combinatorics), (1 + rate)^{time} is a better model.

## Read More
- [An Intuitive Guide To Exponential Functions & e](https://betterexplained.com/articles/an-intuitive-guide-to-exponential-functions-e/)
- [Common Definitions of e (Colorized)](https://betterexplained.com/articles/definitions-of-e-colorized/)
- [Q: Why is e special? (2.718..., not 2, 3.7 or another number?)](https://betterexplained.com/articles/q-why-is-e-special-2-718-not-other-number/)