Regarding getting married. The key date is December 31st. If you are married when the calendar years ends the IRS treats you as being married for the entire year.
Having to pay a small amount at the end of the year is fine. You can make fine tuning adjustments during the year by changing the number of allowances. Getting a huge refund is a loan to the government. Owing a lot of money may result in penalty.
The tax problem with getting married is that the withholding at the single rate for most of the year can be an issue when you file as married.
One way to avoid the underpayment penalty is to make sure you meet the safe harbor rules:
If you did not pay enough tax throughout the year, either through
withholding or by making estimated tax payments, you may have to pay a
penalty for underpayment of estimated tax. Generally, most taxpayers
will avoid this penalty if they either owe less than $1,000 in tax
after subtracting their withholding and estimated tax payments, or if
they paid at least 90% of the tax for the current year or 100% of the
tax shown on the return for the prior year, whichever is smaller. There are special >rules for farmers and fishermen, certain household employers and certain higher income >taxpayers. Please refer to Publication 505.
You will need to check the rules for high income tax payers to see if you fall under those rules.
The "100% of the tax shown on the return for the prior year" rule is proabably easiet to understand:
- Look at both forms after you file your taxes in April 2015.
- Look for your total tax, not what you owe or your refund amount, but your total tax.
- Add them.
- Make sure that all your withholding in 2015 exceed that total. Then even if you owe money in April 2016 you will avoid the penalty.