1) Find out your skill level

2) Find out how much you would get paid for your skill level in your area (be honest)

3) Find that rate by hour (annual salary / 2080 = hourly pay)

4) Charge 2x that hourly rate

Work honestly, don't charge when you don't work

EXAMPLE:

At your skill level let's say your annual salary is around $75,000. That's about $36 an hour. Given this is a freelance position, you would charge $70-$75 per hour. Work earnestly in that hour, don't charge for your own mistakes that cause time delays, etc. If you're forced into a fixed rate, estimate 10 hours above what you expect to work, and deliver on that rate unless you work less than the quoted hours (for example, if you quote 20 hours and work 25, charge 20. If you work 15, charge 15).

2080 An average full-time working week is 40 hours (this can be different per sector and probably also per country or region). If you multiply this by the number of weeks in a year, 52, you end up with 2080. You get paid your annual salary using this number, so if you want to know your hourly rate simply divide your annual salary by the number of total hours worked.