8 years of experience, doing mostly frontend dev, some UX design, and occasionally some full-stack.

Rule of thumb: Whatever you were making as a full-time employee, divide your annual salary by 2,000 to get your hourly rate, then multiply by 2-3x to cover your overhead costs (rent, equipment, health insurance), as well as client uncertainty (won't pay (on time), time between projects, etc.).

Contracting for public tech companies / big entities, I shoot for $250/hr and am happy with anything above $175/hr. Contracting for smaller companies / startups, absolute minimum $75/hr, and only if I really like them.