There are limits. From reading the instructions of the various forms and the various IRS publications and topics (of which there were quite a few) you run into some reductions on your deductions if the rent is far enough below "market value." Market value for my home seemed to be on the low side of what I see around here, so even though I am renting it out super cheap, it was still close enough to market value for the deduction to be substantial. Likewise, the total deductions are limited by the income, but up to a point you can still claim a net loss from the venture.
And yea, so, there are a ton of forms. And I won't claim to understand them and the deeper I go the more I don't think anyone can credibly claim to understand them.
But I think this is what you're looking for from publication 925:
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Definition of passive activity loss. Generally, your passive activity loss for the tax year is the excess of your passive activity deductions over your passive activity gross income. See Passive Activity Income and Deductions , later.
Passive Activity Loss
Generally, the passive activity loss for the tax year is not allowed. However, there is a special allowance under which some or all of your passive activity loss may be allowed. See Special $25,000 allowance , later.
A rental activity is a passive activity even if you materially participated in that activity, unless you materially participated as a real estate professional. See Real Estate Professional under Activities That Are Not Passive Activities, later. An activity is a rental activity if tangible property (real or personal) is used by customers or held for use by customers, and the gross income (or expected gross income) from the activity represents amounts paid (or to be paid) mainly for the use of the property. It does not matter whether the use is under a lease, a service contract, or some other arrangement.
Special $25,000 allowance. If you or your spouse actively participated in a passive rental real estate activity, the amount of the passive activity loss that is disallowed is decreased and you therefore can deduct up to $25,000 of loss from the activity from your nonpassive income. This special allowance is an exception to the general rule disallowing the passive activity loss. Similarly, you can offset credits from the activity against the tax on up to $25,000 of nonpassive income after taking into account any losses allowed under this exception.
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I think I know what this means, but for all I know it applies only to beet farmers in the pacific northwest.