income tax witholding - working a partial year

[EliteZags]

in short I got to take a nice break from work all year and just started again this month, estimate will earn something close to 45-50K this year and want to avoid overpaying on taxes and having a big refund

payroll doesn't have a way to alter federal tax withholding percentage, so I figured increasing # of allowances was the only way to reduce it, 1st paycheck I entered 5 allowances and ended up with 29% in taxes (Fed/CA state), 2nd one I increased to 10 and it lowered to 26%. Should I go even higher on the allowances to minimize witholding/refund?
Not going to contribute to 401K til Jan since there's no match yet and really no 2019 tax advantage for me since I will be in the 12% federal bracket after the 12K standard deduction right? planning to max HSA/Roth

just trying to figure out what withholding percentage I should be shooting for here so I'm not over/underpaying


here are the percentages from latest check with 10 allowances:
Fed Withholding- 10%
Fed MED/OASDI 7.5%
CA Withholding/OASD- 8.3%

[Philociraptor]

The IRS has a nice calculator for that.

[seattlecyclone]

The Medicare/SDI portion is fixed. Changing your allowances won't make a difference there. The federal percentage already seems in the right general ballpark if you're making $50k this year. If you're single that would probably put you right around the border between the 12% and 22% brackets, so 10% effective rate sounds about right. Not sure about your state taxes.