Since there is no sign that the tax laws will change for 2019, you can take the amount you owed for 2018, and assuming that your own income situation does not change much, that is probably the amount you will owe next year if you don’t change your withholding. Add a minimum, you need to have that much extra taken out of your paychecks to avoid a penalty for 2019. If there is a big discrepancy between the amount you owed and the additional amount calculated on the W-4, then you might want to try calculator on the IRS website.
As long as you’re filing jointly, and aren’t planning a separation or divorce, then it doesn’t matter which paycheck pays the extra tax. Or, you could make estimated payments instead. Estimated payments are due April 15, June 15, September 15, and January 15.
