OK ... this thread is almost a year old ... and covers the tax law change period which happened in February 2018 ... the lower tax rate means the withholding was lower starting in Feb 2018 than in the prior years. Also a bonus will also skew the withholding as well as when you reach the SS limit. Also the poster mentioned there was a change in payroll companies ... so checking the withholding allowances to see if they transferred correctly or filling in a new W4 would be wise.
Now in the end ... all your income and withholding is entered on the tax return ... and once the tax is calculated if you paid in too much you get a refund.
