I can provide you with some advice on how to fill out your W4 for 2021...Given what you stated in the first "scenario" question, if you believe this will not change, you obviously would not want much at all withheld from your taxes as your tax liability will most likely be zero (again, going along with what you say above and assuming you don't have other sources of income).
I suggest you do the following:
Based on your hourly rate and your husband's hourly rate for W2 income ($25k and $3k, respectively), if your hourly rate has not changed with this new job you've taken starting in March, and your hours per week are to be the same (ex.: 25,000/52 weeks/40hrd = $ 2.019/hr.), then you can expect to make the same annually, same goes for your husband. If you are getting a bump up in your hourly rate, for ex. say, to $18.50/hr., then your annual gross income for this new role will be approximately $ 31,820 (18.50*40hr*43 weeks). What ever your hourly rate is for this new role, do that same calculation just by substituting whatever the hourly rate is with the 18.50 I "plugged" in. This will give you your approximate annual gross income (once you add your husband's expected gross income for the year).
Once you've done this calculation for the new rate of pay, use the tax table below to try to figure out what tax rate you and your husband fall into (AFTER the reduction for Standard Deduction for MFJ of $18,650). So, lets just use the above for the example...
$31,820 + 3,000 = 34,820 - 18650 = $ 16,170 - THIS WOULD BE YOUR TAXABLE INCOME
Following the information from the IRS 2020 Tax Table found here 2020 IRS Tax Table , your taxable income would be $1,618.00. Again, this is assuming nothing else existing on your return.
SO, when you fill out the W4, if you need or rely on or just like to have every dollar you make go into your net paycheck, you want to have as little withheld as possible. This is called "breaking even" to your expected taxable income.
Instructions for filling out a "break even" W4:
Step 2: Check off Box "C" if you only have these 2 jobs and they are both W2 jobs (ie - he does not get paid via 1099)
Step 3: ZERO on all 3 lines
Step 4: Since your Federal Income Tax plus FICA (SS & Medi) will be a total of approximately $3,666 (calculation from a tax tool found
here Figuring Your Total Tax Federal and FICA ) , you do not need to withhold too much, therefore I would recommend you
do the following:
4(a) - ONLY if both jobs are W2, enter ZERO. If husband's job is 1099, that will be your call on this line.
4(b) - THIS LINE IS OPTIONAL AND NOT A "you'd better be exact" as this W4 is yours! So, enter as if you were not
taking the SD but Itemizing, even though you're not, this is only for calculation purposes for your employer's HR
department. For your tax situation, I would recommend you enter $25,000 here and this will give you more in
your paycheck, less of a refund, but still a refund and you won't owe.
4(c) - ZERO
I hope this helps. For your State, if it still allows an actual "allowance" number, I suggest you enter "6". NOW, if during the year, your situation changes - say, you get a huge pay increase - you will want to go to your employer's HR Department and fill out a new W4 to reflect updated pay.
