TIRA to backdoor Roth tax implications

2020 was the first year I ever had a traditional IRA (TIRA) . My financial advisor recommended that I start it in 2020 to convert it to a backdoor Roth IRA (I already had a Roth IRA).

 

My income in 2020 exceeded both the Roth contribution limit and the deduction for TIRA contribution limits. So, the money that went into the TIRA is post-tax dollars. 

 

It appears that when I enter the 1099-R data into Turbotax, I am taxed on the amount that converted from TIRA to Roth IRA. But since I that TIRA contribution was pre-tax, this seems to tax the TIRA contribution a second time when it converts to Roth IRA.

 

Is that correct? Does that make sense to anyone?

 

I am beginning to think that my financial advisor gave me bad advice, for he explained when we did it that I would only be taxed on whatever gain occurred during the one day it was in the TIRA, which was pennies. 

 

Thank you for your time and be well.