Originally Posted by Jughead135

Any time you do a conversion rollover (which is what you’re doing for a back door Roth), you have to prorate your pre-tax and after-tax balances across ALL (traditional) IRAs you own—you cannot just convert the after-tax portion. Thus, you’ll pay current-year tax on any pre-tax portion so converted.

Assuming that avoiding current-year tax is your goal, you have to keep your traditional IRA(s) empty, so that when you make your contribution then convert it to a Roth, the pre-tax proration is zero.