text: In your example, the quoted "3%" refers to interest earned for an entire year.  You cannot expect to earn 3% for only one month.  Each month may be as short as 28 days, or as long as 31 days, so the amount of interest is different each month.  If you calculate the interest each month for a year and add the 12 amounts, you will find the total really is 3% for the entire year (except for possibly a few cents difference because of rounding - our monetary system does not recognize fractions of a cent).\n\n"3%" REALLY IS 3% in business, but your understanding of simple mathematics needs a little more work.