• Income below Roth limit：after tax money buys Roth IRA
• Roth 401K: change job => rollover to Roth IRA
• 401K: change job => Rollover to IRA. Convert before tax money from IRA to Roth IRA. Pay tax.
• Above Roth income limit: After tax money buys IRA. Record after tax base in form 8606. Convert from IRA to Roth IRA. Use form 8606 to calculat taxable amount.

Simple 8606 calculation with 401K rollover $2，after tax contribution $2 (Assuming no gains) :

1. convert to Roth $2: $1 towards income base, $1 tax free, $1 after tax base carry over, IRA = $2, Roth IRA = $2 
2. convert to Roth $4: $2 towards income base, $2 tax free, $0 after tax base carry over, IRA = $0, Roth IRA = $4

Backdoor Roth tax year:

• 2020年的contribution，可以截至4/15/2021税后放入 IRA。需要填2020年8606 record pre-tax base。
• convert：现在至12/31/2021，算2021年的form 8606，2022年报2021税时用。

Backdoor 最吃亏的是：

• After tax money funded IRA but did not convert to Roth. 然后一大堆gains taxed as ordinary income.
• Use before tax money converted at high, then market is down
• Roth IRA lost no tax deduction.

只有转之前market大跌除外。

links：

• Backdoor Roth IRA：1）https://www.whitecoatinvestor.com/backdoor-roth-ira-tutorial/。2） https://www.investopedia.com/how-to-set-up-a-backdoor-roth-ira-4584775?utm_campaign=quote-yahoo&utm_source=yahoo&utm_medium=referral。
• Mega backdoor Roth IRA https://www.nerdwallet.com/article/investing/mega-backdoor-roths-work