Interest on 1,000 at one percent, per month

Interest Per month
Percentage 1%
Amount 1,000

One percent of 1,000
1% of 1,000 is 10

Month
Interest for month is amount

One month
10 x1 month is 10
10 x2 months is 20
10 x3 months is 30

One year 
10 x12 months is 120