Since your financial planner knows your entire financial situation follow their advice.
Thats what i did when I worked and married. I claimed Single to have more taken out. Or you can try increasing the withholding by adding a fixed amount to it. Or send in extra estimated payments to cover the higher tax when you both have income.
Thank you for the question. Your financial advisor probably has significantly more information about your joint financial picture then this question presents.
When your W-4 Part 1 filing status is checked as Single, income taxes are withheld at a higher rate then if the filing status is Married filing jointly. Your financial advisor is most likely attempting to account for income other then on the W-2.
Assuming this is what your financial advisor is recommending, I would also recommend that you account for most of the additional income by using these two resources: