With compound interest (almost always the case today), at the end of each month you owe what you did at the beginning plus another 2% of that - that is, (1 + 0.02) or 1.02 times what you originally owed. Then after the next month you owe 1.02 × 1.02 × the original amount, and so on.

The general formula is (1+R)^N × P where P is the principle, N the number of periods, and R the rate per period.

Good Hunting!
RD