Business expenses are tax deductible, however the expense must be for "business," and you are not being reimbursed for travel by your employer. For example, if you spent $1,000 to go to a conference that lasts 2-days. ALL of your expenses are related to the conference, i.e, food, hotel, air, etc. went towards the conference, all is deductible. If however, you spent an extra night, then only 2/3 of the expenses are deductible. It is also a red flag for a possible audit.
Hope this provides some help.
