Your workers comp premium is driven by payroll. The more payroll you have, the higher the premium you pay. When you start your policy, you will make a good-faith estimate of your anticipated payroll for the coming 12 months. Your insurance company will provide you a good-faith estimate of the premium you will pay. At the end of the policy period, your insurance carrier has the right to audit your payroll to determine your actual payroll. If your originally estimated payroll is less than your actual payroll, you will owe the insurance company money. If your originally estimated payroll is more than actual, you can anticipate a refund subject to minimum premium charges.
Your best strategy is to accurately predict your payroll at policy inception to avoid over or under paying. If during the policy period you determine your prediction will not hold up, report in with your insurance company and adjust accordingly.