If you paid for the room, you enter it as if you made a cash donation to the charity. If audited, you would need a letter from the charity saying something like "Thank you for donating a weeks' accommodations at _____." The letter does not have to prove the price, you do that from your own records. But you need proof that the donation was accepted by the charity and the costs were paid on behalf of the charity.
If this is a hotel you own and you gave away the accommodations for free, you can't deduct anything. Your tax "reduction" is the fact that you have less taxable income to report. OR, you can book the revenue as if you received it in cash, then deduct the same amount of cash as a donation.
You can deduct out of pocket costs that you paid in order to provide the room to the charity, but I don't know how you would reasonably prove that a few dollars of the maid's salary was allocated to this specific room, or any other hotel staff or utilities, etc.
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IRS Pub 526
Unlike cash, you cannot deduct the cost of a stay that you donate to charity. Donating a stay in your property is considered “right to use property”. This falls into the category of “partial interest in property”. The IRS is very clear that this is not deductible. See IRS Publication 526.)
You can't donate the use of something.
Partial Interest in Property
Generally, you can't deduct a charitable contribution of less than your entire interest in property.
Right to use property.
A contribution of the right to use property is a contribution of less than your entire interest in that property and isn't deductible.
You own a 10 story office building and donate rent free use of the top floor to a charitable organization. Because you still own the building, you have contributed a partial interest in the property and can't take a deduction for the contribution.
Mandy White owns a vacation home at the beach that she sometimes rents to others. For a fund-raising auction at her church, she donated the right to use the vacation home for 1 week. At the auction, the church received and accepted a bid from Lauren Green equal to the fair rental value of the home for 1 week.
Mandy can't claim a deduction because of the partial interest rule. Lauren can't claim a deduction either, because she received a benefit equal to the amount of her payment.
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And think of it this way. You will get the deduction by claiming less income. Which might work out better since you might not have enough total deductions to itemize. If you want to claim a discount, refund or rebate you have to first include the amount as income.