Pet rent is a recurring monthly charge a landlord adds to the rent for the right to keep a pet in the unit. It is separate from a one-time pet fee, which you charge once and keep, and from a refundable pet deposit, which you hold against pet damage and return at move-out minus any documented deductions.
In practice
Say base rent on a unit is $1,500 and you allow one dog for $35 per month in pet rent. The tenant now owes $1,535 each month, and that full amount is the rent. Over a 12-month lease the pet rent alone adds $420 (35 × 12). If you also collect a $300 refundable pet deposit, that $300 is not income while you hold it: it sits with the security deposit and is only yours to keep if the dog causes damage you can itemize. The $35 monthly charge, by contrast, is rental income the day it is paid, and it shows up on your books every month whether the dog ever chews a baseboard or not.
That distinction is the whole point of the three structures. A deposit is a liability you are holding. A one-time fee and monthly pet rent are both income. Keep them on separate lines so you never accidentally treat a deposit as money you earned.
Why it matters to a small landlord
Pet rent is taxable income, so it belongs in your rent total and flows through to your Schedule E the same way base rent does. If you fold a deposit into that total by mistake, you overstate income and lose track of what you owe back at move-out. Decide up front which dollars are a fee, which are deposit, and which are recurring pet rent, and record each on its own line. For the deposit side specifically, the rules on holding and returning that money are stricter than most landlords expect, so it helps to keep a clean security deposit paper trail from the day the lease is signed.
One caution that overrides everything above: some states limit how much you can charge in pet fees and deposits, and assistance animals are not pets under fair housing rules. You cannot charge pet rent, a pet fee, or a pet deposit for a service animal or an approved emotional support animal. Read your state's statute before you set a number, and treat accommodation requests as their own process.
Put your pet terms in writing as a lease addendum so the amount, the deposit, and the rules are signed and dated, not a verbal side deal. At move-out, the line between a refundable deposit and a kept charge comes down to whether the pet caused real damage or only normal wear and tear. And if a tenant requests an assistance animal, handle it as a reasonable accommodation, not as a pet, and drop the pet charges.