How to estimate PEC?

Do you know how to estimate the Special Payment on Account (PEC) and it's payment deadlines? The Special Payment on Account (PEC) it's due by all the taxable people framed at the IRC's normal tax system. It's deductable from the concerned financial year and from the 6 following years. The PEC is estimated over the business volume from the previous year with a minimum of 1.000 € and an upper of 1.000 euros + 20% from the surlus with the limit of 70.000 euros. The PEC payment can be done in a single delivery at march 31 or in 2 semestral deliveries – at march 31 and at october 31.