There
are three main reasons that could happen.
The first
is that the more income you have, the higher the tax bracket you may find
yourself in. The higher the bracket, the bigger percentage of your income is
taxed. Even if you did not jump into a new bracket, the entire amount of
the second W-2 is being taxed at the higher rate instead of incrementally like
the first. Here are the brackets for 2017:
https://taxfoundation.org/2017-tax-brackets
The
second is withholding, the amount your
request your employer to withhold on your W-4. There are three choices you can
make on line 3: Single, Married or Married but withhold at a higher Single
Rate. If you choice the first or third option, they will withhold more than if
you choose Married.
On
line 5, you tell how many allowances you with to claim. If you choose zero,
they will withhold the most based on the tables (see Pub 15 link below). The
more allowances, the smaller the refund, BUT, you will get a little more in
each paycheck. In that way, you can choose if you prefer to have more money in
your paycheck or at the end of the year in your refund.
If you
have a second job that is part time or makes little per week, the table will
not direct the employer to withhold amounts based on your entire income.
Please
see the links below for more information. The first is a copy of Form W-4. The
second shows the withholding tables for
2016, starting in Section 17, Wage Bracket
Method.
The third is that your increased
income may have decreased any income-based credits you were receiving.
