##### Charles Wang, Data Scientist at Noodle Education

Depends on whether you are dealing with simple or compound interest.

The equation for simple interest is:

I = P(1 + rt)

Do the algebra:
*Divide both sides by the principle (P)
*Subtract one (1) from both sides
*Divide both sides by time (t)

That gets you the interest rate, (r).

For compound interest:

I = P(1 + r)^t

*Divide both sides by the principle (P)
*Take the t-th root of both sides
*Subtract one (1) from both sides

Good luck.