The backdoor Roth funds a non-deductible Traditional IRA contribution, then converts to Roth. IRS pro-rata rules blend all Traditional IRA balances—avoid surprises.
Mega Backdoor
Some 401(k) plans allow after-tax contributions rolled to Roth—separate strategy with higher limits.
Conclusion
Use Form 8606 and consult a CPA if you have existing IRA balances.