The retirement you took out:
First there is a 10% penalty (if early withdrawal-under age 59 1/2) in the total amount (in box 1 of the 1099R)
Then there is ordinary income tax also. You may be in the 25% tax bracket (see below link)
You do get credit for the 20% (in box 4 of 1099R) paid in.
However, I just showed you that the distribution may be costing you 35% (10% + 25%) and only 20% was withheld.
This is the same principle as the W-2 wages, you have money taken out during the year, and then report on your taxes, to help determine if correct amount was taken out. Result is refund or balance due.
A single filer with taxable income of over $37, 650 is in the 25% tax bracket. If you are not a single filer, the link has other filing status. To see what tax bracket you are in for sure see the link below.
https://taxfoundation.org/2016-tax-brackets
