Torontokids has it correct. First year in business, you aren't required to pay anything during the year, but if you expect to be in the taxable range, you may want to anyway. After that, you are required to use your previous year's income as an estimate for the following year. Whatever your business taxes were last year, you are supposed to pay the same this year in 4 quarterly installments. If you don't pay at least that, the government will charge interest on what wasn't paid.