If you have built your business up to the point where you need extra help, congratulations! You now get to be an employer. There are additional duties and responsibilities that come along with bringing people onboard your organization. In addition to wages and benefits, you need to calculate the cost of payroll taxes (depending on your state) as well as workers compensation insurance.
Many people try to get around this by making their employees 1099 independent contractors. In most cases, this effort fails miserably after an employee is injured or during the annual workers compensation audit process. If your workers comp program is not set up correctly upfront, you will have an unpleasant surprise waiting for you at the end of the term, which can be a considerable cost that is due and payable within 30 days.
In most states, depending on what your employees are doing, the costs can range from <1% of payroll for sales people to 5% or more for laboratory workers. Costs for this type of coverage are always expressed as a percentage of your annual payroll. For example, if you have $100,000 in annual payroll and your rate is 5%, you will pay $5,000 per year for workers compensation insurance (+fees & taxes depending on your state).