One of the three rules for an accountable plan is that you must adequately account to your employer for your expenses. You adequately account by giving your employer a statement of expense, an account book, a diary, or a similar record in which you entered each expense at or near the time you had it, along with documentary evidence (such as receipts) of your travel, mileage, and other employee business expenses. (See Table 4 in chapter 5 for details you need to enter in your record and documents you need to prove certain expenses.)
You must account for all amounts you received from your employer during the year as advances, reimbursements, or allowances. This includes amounts you charged to your employer by credit card or other method. You must give your employer the same type of records and supporting information that you would have to give to the IRS if the IRS questioned a deduction on your return. You must pay back the amount of any reimbursement or other expense allowance for which you do not adequately account or that is more than the amount for which you accounted.
Information courtesy of the Internal Revenue Service.
