Annual premiums are generally paid in two installments - on April 1 and on September 1. If your payment is late, you'll be charged interest at the Bank of Canada rate as of October 31 of the previous year plus 6%. You can also be charged with the costs of your workers' injury claims during the time your premium payment is overdue. Provide an adequate payroll estimate: If your actual payroll is higher than the estimated payroll by more than 50%, a 6% underestimate penalty will be charged. When the actual payroll is less than 50% of the estimated payroll the overestimate credit is given. You can revise your payroll estimate at anytime throughout the year.