Your Spouse Started a Business. What Does That Mean for Your Taxes?

How a new business can affect household tax planning, withholding, and the records couples need to review.

A paycheck arrives with the tax already handled. Your employer calculates it, withholds it, and sends it to the IRS before the money reaches your account. Business income does not work that way, because it lands in the bank whole, with nothing set aside for the federal government. That one difference is behind most of the surprises couples report in their first year of business ownership. The income is usually welcome news, but the return that follows asks both of you for a few new decisions, even when only one name is on the business.

Most couples face the same handful of questions in the same order. The first is what changes in the tax math once one spouse is self-employed. The next is how to adjust paychecks and quarterly payments so April does not bring a bill, and after that come the deductions, filing choices, and records that deserve a conversation at the kitchen table. The numbers here are for the 2026 tax year. Since it is late October, there is still time to act before December 31 and before the January 15 payment date.

A second tax appears, and it is not the income tax

Income tax is the one most people expect. The one that surprises them is self-employment tax, which is the Social Security and Medicare tax that an employer and employee would normally split. The IRS sets the self-employment tax rate at 15.3%, and it applies once you have net earnings of $400 or more as a self-employed person. Net earnings means profit after business expenses, not the money customers paid you. The tax is applied to 92.35% of net earnings from self-employment, so the 15.3% rate is not charged on every dollar of profit.

Consider a spouse who earns $40,000 in net profit this year. Multiply $40,000 by 92.35 percent to get $36,940, then multiply that by 15.3 percent, and the self-employment tax is $5,651.82. Half of that amount, $2,825.91, is then deductible when figuring income tax, which softens the blow slightly. A useful shortcut is that every $1,000 of profit carries about $141 of self-employment tax before any income tax is added. A couple in the 12 percent bracket and a couple in the 22 percent bracket should both plan to set aside well more than the income tax rate alone suggests.

Two details matter for married couples. If both spouses have self-employment income, each must file a separate Schedule SE, so a spouse's wages from a job are counted on their own and do not reduce the tax owed on the other spouse's profit. The Social Security portion applies only up to $184,500 of earnings in 2026, while the Medicare portion has no ceiling. An additional 0.9% Medicare tax applies to self-employment income over $250,000 on a joint return. Most new businesses will not reach either threshold in the first year, but a high earning household with a profitable side business might.

Who owns the business matters more than most couples expect

When one spouse owns and runs the business alone, the filing is straightforward, because the profit goes on one Schedule C in that spouse's name and one Schedule SE follows it. If only one spouse participates in the business, all of its income counts as the self-employment earnings of the spouse who carried it on. The other spouse appears on the joint return as usual and does not owe self-employment tax on that profit. Matters change once both of you work in the business and share in the profit. The IRS treats a business jointly owned and operated by a married couple as a partnership filing Form 1065, unless the spouses elect qualified joint venture status or operate in a community property state.

The qualified joint venture election lets spouses report as two sole proprietors, each with a Schedule C and a Schedule SE, instead of filing a partnership return. The requirements are that the spouses are the only two members, both materially participate, they file a joint return, and both agree to the election. Income and expenses are divided between the two schedules according to each spouse's interest in the business, so the split should reflect who owns it and who does the work. A business operating in the name of a state law entity generally falls outside the qualified joint venture rules, although couples in a community property state may qualify even with a husband and wife LLC. If your business is an LLC, ask your preparer before assuming the election is available to you.

A different arrangement is for one spouse to own the business and employ the other. Wages paid to a spouse who works in the business are subject to income tax withholding and Social Security and Medicare taxes, but not to federal unemployment tax. The job must be a bona fide one, the pay must be reasonable for the work performed, and the business needs documentation. Proper documentation lets you support the deduction if the IRS examines wages paid to family members, which in practice means a written job description, time records, and proof of payment. Payroll brings its own filings and deadlines, so it is worth setting up correctly from the first paycheck.

How to adjust withholding, step by step

Withholding is the simplest tool, because it uses a system that is already running. The spouse with a job can ask the employer to take out more, and the extra tax is credited to the couple's joint return. Federal income tax withheld from wages is generally treated as paid evenly throughout the year, while estimated payments count on the date they are made. That means increasing withholding late in the year can cover a shortfall from earlier quarters. Many couples lean on withholding in the first year of a business for exactly that reason.

Step 1. Estimate the business profit for the year. Start with expected revenue, subtract the expenses you can document, and use that result, not gross sales, as your profit figure. If the business opened partway through the year, count only the months since it opened. A cautious estimate is the better choice here, because overestimating means the extra comes back as a refund, while underestimating can bring a penalty. Write the number down along with the assumptions behind it so you can revise it in January.

Step 2. Run the numbers with the IRS tools. The Tax Withholding Estimator at IRS.gov/W4App can show whether you need to change your withholding, and people with self-employment income are directed to the worksheets in Publication 505 to decide whether to pay estimated tax. If you file jointly and both of you have net earnings from self-employment, each of you completes a separate worksheet. Before starting, gather your 2025 return, a recent pay stub from the working spouse, and your profit estimate, because the tools ask for all three. The result is a projected total tax for 2026 and a figure for how much of it withholding already covers.

Step 3. Decide how the gap will be paid. The difference between projected tax and expected withholding can be closed with extra withholding, quarterly estimated payments, or a mix of both. If you choose extra withholding, divide the amount you want withheld by the number of paydays left in the year. The IRS uses this method in its own example, where a couple divides an additional $4,459 by 49 remaining paydays and the spouse enters $91 in Step 4(c) of Form W-4. The couple is free to split the amount between both spouses' paychecks if both have jobs.

Step 4. Give the employer a new Form W-4. Only the spouse who is an employee can do this, and the additional amount goes in Step 4(c). An employer must put a revised Form W-4 into effect no later than the first payroll period ending on or after the 30th day after you submit it. A form submitted now may therefore affect only the last few paychecks of 2026, which is still useful because of the even treatment described above. Employers cannot accept a payment from you to cover estimated tax, so the W-4 is the only route for adding tax through a paycheck.

Estimated payments, due dates, and safe harbors

Estimated tax pays not only income tax but also other taxes such as self-employment tax. Individuals, including sole proprietors, generally must make estimated payments if they expect to owe $1,000 or more when the return is filed. The four installments are due April 15, June 15, September 15, and January 15, which makes the final 2026 installment due January 15, 2027. A penalty can apply for missing an installment even when you are due a refund at filing, so the dates matter even for households that expect to come out ahead overall.

Timing works differently for a business that opened partway through the year. Income that first arrives between September 1 and December 31 makes January 15 of the following year the due date, so a spouse who launched in the fall may owe a first payment only in January. The IRS also notes that you may pay the full amount due on the first quarterly due date instead of making four payments. When income is uneven, Publication 505 offers an annualized income installment method that sizes each installment to the income received by that point. It is figured on Form 2210, Schedule AI, and is worth asking your preparer about if the business earns most of its money late in the year.

Penalty protection comes from meeting one of two targets. The amount you must pay is the smaller of two figures: 90 percent of the 2026 tax, or 100 percent of the total tax shown on your 2025 return. If prior year adjusted gross income was more than $150,000, or $75,000 for married filing separately, the prior year target rises to 110%. The prior year target is attractive for a new business because it is a known number that does not depend on forecasting profit. Withholding counts toward either target, so the working spouse's paycheck does part of the job automatically.

A short example shows how this works. Suppose the couple's 2025 joint return showed total tax of $14,000 and adjusted gross income below $150,000. Their 2026 target under the prior year method is $14,000, or $3,500 per installment, and if the working spouse's employer will withhold $11,000 for the year, the remaining $3,000 must come from estimated payments or extra withholding. With 2025 adjusted gross income above $150,000, the same target would be 110 percent, or $15,400. Meeting the target prevents the penalty but does not prevent a balance due in April if the business was profitable, so cash for the difference should still be set aside.

Marriage adds a few wrinkles to the prior year test. Married taxpayers can make joint estimated payments even if they later file separate returns, and in that case either spouse can claim all of the amount paid, or each can claim part of it. If you filed separate returns last year but plan to file jointly this year, your prior year tax is the total shown on your two separate returns. If you filed jointly last year and will file separately this year, each spouse uses a share of the joint tax figured with a formula in Publication 505. Couples near a change in filing status should have their preparer run both versions before choosing.

Deductions and credits that begin to matter

Money spent before the doors open follows its own rule. You can deduct up to $5,000 of startup costs in the year the business begins and write off the rest gradually, and the remainder is deducted evenly over 180 months starting with the month the business opens. The $5,000 shrinks once total startup costs pass $50,000 and disappears entirely at $55,000. For example, $8,000 of qualifying startup costs produces a $5,000 deduction in the first year, with the other $3,000 spread over the following 15 years. Costs paid after the business is operating are ordinary expenses deducted normally, so the date the business began should be written down.

A home office deduction is available only for space used regularly and exclusively for the business. The simplified method allows $5 per square foot for up to 300 square feet, which caps the deduction at $1,500, while self-employed taxpayers using the regular method figure the deduction on Form 8829 and claim either method on Schedule C. Because the deduction sits on the business schedule, it applies whether or not the couple itemizes. A dining table that doubles as a desk generally will not qualify. Measure the space, photograph it, and keep the measurements with your tax records.

Health insurance deserves a careful look in a household where the other spouse has a job. The IRS does not allow the self-employed health insurance deduction for any month you were eligible for an employer subsidized plan, including your spouse's, even if you did not participate. The test is applied month by month, so a spouse who gains or loses employer coverage in the middle of the year can change the answer for part of the year. The deduction also cannot exceed the profit from the business, so a business with a loss produces no deduction. The deduction is worked out on Form 7206, and the premium statements should be kept with the return.

Two larger opportunities are retirement contributions and the qualified business income deduction. For Solo 401(k) and SEP plans the 2026 contribution limit is $72,000, and the 401(k) employee deferral limit is $24,500. The practical ceiling for a new business is usually its profit rather than the plan limit, so the plan type and timing should be chosen with a preparer before year end. Recent legislation made the qualified business income deduction permanent, and beginning in 2026 someone with at least $1,000 of qualified business income from an active business may claim a minimum deduction of $400. The 2026 standard deduction for joint filers is $32,200, and business deductions reduce profit before that standard deduction is applied.

If the business loses money in the early years

Many new businesses lose money at first, and on a joint return a business loss can reduce the couple's other income, including the other spouse's wages. That benefit is available only when the IRS regards the activity as a business rather than a hobby. If the activity shows a profit in three of five consecutive years, the IRS presumes it is carried on for profit, and a new business without that history is judged on facts such as whether it is run in a businesslike manner with complete and accurate books and records. A taxpayer can file Form 5213 to postpone the profit determination, but filing it extends the statute of limitations for the years in the postponement period, so it should be discussed with a preparer first. A loss year also removes the health insurance deduction described above.

Filing status and shared responsibility

When you file a joint return, the law makes both you and your spouse responsible for the entire tax liability. That responsibility extends to additional tax the IRS later determines is due, even when it arises from the other spouse's income or deductions. Relief exists in some situations through Form 8857, but it depends on the facts and is never automatic. The spouse who does not run the business therefore still needs to understand the profit figures, the payments that were made, and the records behind the deductions. Filing separately is an option, but it changes thresholds such as the $75,000 line for the 110 percent safe harbor, so it should be modeled before the decision is made.

Records both spouses should review

Good records are what turn a tax position into a supportable one. The IRS says to keep records supporting income, deductions, and credits until the period of limitations for that return runs out, which is generally three years, extends to six years when more than 25 percent of gross income is left off a return, and runs four years for employment tax records. Employment tax records should be kept for at least four years after the tax is due or paid, whichever is later. A short review once a quarter, done together, keeps small gaps from becoming problems in January. These items belong in the shared file:

• Income records, including invoices, bank deposits, 1099 forms, and payment platform statements, matched against one another so nothing is missed.

• Expense receipts, a mileage log, and statements from a business only bank account and card.

• The date the business began and a list of startup costs paid before and after that date.

• Home office measurements and photographs, plus household bills if you use the regular method.

• Confirmation of each estimated payment, with the date, amount, and the spouse whose account paid it.

• The working spouse's pay stubs and W-4, to confirm that added withholding took effect.

• Health insurance premium statements and a note of which months employer coverage was offered.

• Retirement plan documents and contribution records, and payroll records if a spouse is an employee.

Keeping personal and business spending in separate accounts is the habit that makes everything above easier. A business account and card create a clean trail for the preparer and for any later question from the IRS. Mixed accounts force someone to sort every transaction by hand, and errors in that sorting tend to cost money. Decisions about estimated payments and withholding are worth recording in a few lines, since both spouses are responsible for the return.

A calendar from here

Before December 31. Complete the projection described above while paychecks remain, and submit a new Form W-4 with an added amount in Step 4(c) if there is a gap. Decide whether a retirement plan makes sense for the business and talk to your preparer about timing. Review which business expenses will be paid this year, collect the 2026 records into one folder, and mark each month on which employer health coverage was available to either of you. Doing this in November leaves room to fix problems that would be hard to fix in January.

January 15, 2027 and filing season. The fourth estimated installment for 2026 is due January 15, 2027, and a calendar year taxpayer who files the return and pays the full tax liability by January 31 does not have to make that January payment. Filing early with a full payment can therefore replace the last installment for couples whose records are ready. The return itself is due April 15, 2027, with the business reported on Schedule C and Schedule SE as described above. Generally the IRS can figure any underpayment penalty for you, and a prepared Form 2210 is the tool for anyone who wants to show a different amount.

A new business changes a household's tax picture in several small ways at once, and none of them is difficult when handled in order. The working spouse's paycheck, the quarterly payments, the deductions, and the records all connect, so it helps to review them together instead of treating the business as one spouse's project. The information here reflects federal rules for the 2026 tax year and is general in nature, not advice for a specific household, and state income tax, sales tax, and local license rules are separate matters. A conversation with a CPA or enrolled agent early in the first year costs far less than a penalty or a missed deduction.