Total Basis for Backdoor Roth IRA

[himanshu983]

For the last 4 years, I have been performing backdoor Roth IRA.

I contributed the max allowed ($6500/$7000) AFTER-TAX dollars to Traditional IRA, and then converted all of that to Roth IRA each year. I have an $ amount in Total Basis (including in prior returns).  Should the Total Basis always be $0?  Have I been doing it wrong all these years?