How to calculate the daily late fee?

Question

Due to my ignorance, I owe the mobile service provider $701. The penalty is 3% per day.

That means on day 1, I should pay

$701 + 701\times0.003$

On day 2, I should pay

$701 + 701\times0.003 + (701 + 701\times0.003) \times 0.003$

and so on.

I learned a lesson that I should pay every bill as soon as possible. I also want to lean some math here:

1. How to calculate the fee until a certain day, say 40 days later?
2. What's the amount of the penalty fee till that day?