“My husband and I are filing separately. I have a business out of my home. When calculating home office utilities, do I split them in half since we are filing separately?”---->I guess so;you need to file separate Sch C /Sch SE(as long as your portion of netearnings on Sch SE line 4 is $400 or exceeds $400).You need to pay separate quarterly estimated taxes as long as you are filing as a sole proprietor and/or a self-employed individual, you generally have to make estimated tax payments if you expect to owe tax of $1,000 or more when you file your return.If you are filing as a corporation you generally have to make estimated tax payments for your corporation if you expect it to owe tax of $500 or more when you file its return.However, you do not have to pay estimated tax for the current year if you had no tax liability for the prior year ;you were a U.S. citizen or resident for the whole year ;your prior tax year covered a 12 month period.Is your business jointly owned and operated by you and your husband???If so, then, your business operated by a married couple is generally treated as a partnership for Federal tax purposes, you must comply with filing and record keeping requirements imposed on partnerships and your partners by filing 1065 and Sch C/Sch SE.However, I am not sure if your business is SMLLC, if it is a SMLLC, then, as long ss the only members of the joint venture are a husband and wife who file a joint return, both spouses materially participate in the trade or business, and both spouses elect not to be treated as a partnership. Spouses electing qualified joint venture status are treated as sole proprietors for Federal tax purposes. The spouses must share the businesses’ items of income, gain, loss, deduction, and credit. Therefore, the spouses must take into account the items in accordance with each spouse's interest in the business. The same allocation will apply for calculating self-employment tax if applicable, and may affect each spouse’s social security benefits. Each spouse must file a separate Schedule C to report profits and losses and, if otherwise required, a separate Schedule C/SE to report self-employment tax for each spouse.