Why freelance rates are higher than salaries suggest
An employee is paid for about 2,080 hours a year, with holidays, equipment and half of Social Security and Medicare covered by the employer. A freelancer pays for all of that, and rarely bills every working hour: admin, sales and gaps between projects are unpaid. That is why the calculator asks for billable hours and weeks off, not a 40-hour week.
The tax set-aside is your own estimate. Use the self-employment tax calculator to see the Social Security and Medicare part.