It depends, there are no rules that cover a trip that is exactly 50/50. You will have to decide if your trip was Primarily for Business or Primarily for Personal reasons even if that is 51/49. Here is what the IRS says: (see Publication
463 for more)
If your trip was primarily for business and, while at your business destination, you extended your stay for a vacation, made a personal side trip, or had other personal activities, you can deduct only your business-related travel expenses. These expenses include the travel costs of getting to and from your business destination and any business-related expenses at your business destination.
If your trip was primarily for personal reasons, such as a vacation, the entire cost of the trip is a nondeductible personal expense. However, you can deduct any expenses you have while at your destination that are directly related to your business.
