Assuming your total income is 22,400 + 30,000 = 52,400
For 2020 taxes, subtract the standard deduction for singles, 12,400 from your total income. 52,400 - 12,400 = 40,000. This is your taxable income.
40,000 is within the 12% tax bracket. If all your dividends and long term gains are qualified dividends, then all 22,400 is "taxed" at the 0% capital gains tax rate. If your qualified dividends and capital gains push your taxable income over 40,000, every CG+Div dollar above 40,000 in taxable income will be taxed at 15%.
The tax calculations works like this:
30,000 - 12,400 = 17,600 taxable income using normal tax bracket rates.
The 10% tax bracket for the conversion is the first $9,875. The tax is 9,875*10% = 987.50
Subtract out the 10% income that has already been calculated. 17,600 - 9,875 = 7,725 left to be taxed at the 12% tax rate. 7,725 * 12% = 927.00
So the tax on the conversion is 987.50 + 927.00 = 1,914.50
Your taxable income was 40,000. Your taxable Roth conversion income was 17,600.
40,000 - 17,600 = 22,400 of dividends and capital gains which is "taxed" at 0%.
So, your total tax is 1,914.50 for an effective tax rate of 1,914.50/52,400 = 3.65%