I've searched the internet for hours unable to find an answer to this question. My husband and I are adjusting our W4s now, several months into the year, to reflect that we got married. Because of this, we're using one worksheet as required to fill out the "Two-Earners" section to calculate extra withholding. The instructions are extremely confusing for someone filling it out mid-year. The tables give me wages, but at Line 9, it asks me to divide by the rest of the pay periods left in the year. Does that mean I am only supposed to be calculating the wages from our two jobs between now and the end of the year, or am I supposed to calculate based on our annual wages? Because those are two very different numbers.
If I did it based on our annual wages, then the instruction in line 9, which tells me to divide by the rest of the pay periods for the year (17), would not compensate for the fact that we've already paid some taxes this year out of those annual wages as our single employed selves. That doesn't seem fair. So I'm thinking the right answer is to either divide by the total pay periods for the year (24) to find what should be withheld per pay period (as if we were starting this back in January) or to base it off of wages left this year. The latter, however, seems to produce a very small number as if we were in completely different tax brackets, so I'm concerned about paying too little.
Also can anyone quickly explain to me why this is even necessary? If we both have 0 allowances on our W4s, as is what happens when you fill out lines 1-9 of the Two-Earners worksheet, then why do I still have to withhold more money? What is the extra withholding making up for?
Thanks so much!