You need at least 1.5x ideally 2x your normal rate to make it worth it.
You need to always be selling, probably should make sure you are consistently overbooked if you want to keep contracting sustainably. Otherwise if you focus on one client only and they go poof, you are back in line for a job.
Be prepared to work many many more hours because of the above.
Don’t forget to calculate ALL your costs.
If you can get a monthly retainer for X number of hours for close to your target hourly rate, take it even if it’s a little low. As long as you are good you’ll (probably) never really need to spend X hours. Leaving you with extra billable hours to devote to other clients while still having some guaranteed income. This is one of the only ways to get ahead, aside from charging “book” hours (estimates) rather than actual elapsed hours.
You’ll get stuck in whatever price range you start with so do not lowball yourself. Again, always be selling, and hours are precious, don’t waste them.
It’s a stressful life because you start to have issues taking any time off.