You were probably having more tax withheld than you needed, which will result in a tax refund when you file your tax return. Changing your withholding to head of household status means that you will have less tax withheld from your paychecks. You will get more take-home money each week but a smaller refund at the end of the year.

Your actual tax liability is only calculated on form 1040 at the end of the year, and doesn’t change regardless of how you fill out your W-4. The W-4 is used to determine how much to have withheld from each paycheck so that you will eventually cover your tax liability. If you are under withheld, you owe additional payments before April 15 and may also be assessed a penalty. If you have excess withholding, that is where your tax refund comes from.

Ok ... take a deep breath.   What you put on the W-4 ONLY influences how the employer does the withholding.   It does  NOT need to match what is on your tax return at all.   In fact prior to 2019 HOH was not even an option on the W-4   AND  withholding at single will actually benefit you on the return.  

That said you can hand in a new W-4 form to your employer anytime ... 

Your W-4 form determines how much tax will be withheld from your pay. Use the Tax Withholding Estimator on the IRS web site to figure out what to put on your W-4 form. It will let you adjust your withholding to get the approximate refund amount that you want. Check it again in January. What you need for a full year at the new job might be different from what you need for the rest of this year.

Tax Withholding Estimator

The W-4 only tells you employer how much to withhold.   It is all reconciled on yiur tax return.  If too much was withheld yiu get a larger refund, if not enough withheld you get a smaller refund or no refund at al an might owe tax.

Some people intentionally have too much withheld and use the tax system as a forced savings account which means that the government  has your money interest free,   while others have too little withheld and owe at the end of the year so that they have use of the governments money as an interest free loan.

It all works out on the tan return.

Single has more withheld then HOH so you would get a larger refund, but less paid to you paycheck-to-paycheck, but you get the difference when you file your tax return.

Hoh not being added until 2019 explains a lot.  Thank you and everyone else for the advice and the link.  I'll have to go check that out.