A lot. I don't know exactly how much, but it will be far more than any other year.

Wouldn't it be good to figure this out before claiming to have doubled your salary? When you have a W-2 job, your employer pays a lot of taxes that are not included in your salary. When you switch to 1099 or self-employment, you now have to pay those taxes yourself.

The employer pays 6.2% of wages up to $110,100 for Social Security and 1.45% of wages (no limit) for Medicare. It's small but known quantity.

For next year, you probably want to talk to an accountant about paying estimated taxes. If you drop 20k in taxes to the IRS at the end of the year, they're not going to be happy. In fact, you can get fines for doing that.

These are the problems you want to have.