When it comes to deducting a spouse’s travel costs for business, the rules are very restrictive. Generally, you cannot deduct the spouse’s travel costs unless the spouse is a bona fide employee of the business. This requirement prevents deductibility in most cases.

Even if your spouse is an employee, his or her presence must be for a bona fide business purpose. Generally, a spouse’s presence must be “necessary” to meet the bona fide purpose test and just being “helpful” does not meet the requirement. Being there for goodwill purposes, such as serving as a hostess, is generally insufficient to satisfy a business purpose. An exception to that rule would be if your spouse's presence is necessary to care for a serious medical condition that you have.

If your spouse’s presence does meet the bona fide business purpose rule, then the normal deductions for business travel away from home can be claimed. These include the costs of transportation, meals and lodging, and incidental costs such as dry cleaning, phone calls, etc.

But all is not lost if your spouse does not meet the qualifications. You may still be able to deduct a substantial portion of the trip's costs. This is because the rules don't require you to allocate 50% of your travel costs to your spouse. You need only allocate to him or her any additional costs that are incurred. For example, the single rate for a room is not so different from the cost for double occupancy. If you were driving, no allocation would be required because the cost would be fully deductible even if your spouse did not accompany you. If you used public transportation, only your cost would be deductible. Any meals and separate costs incurred by your spouse would not be deductible.