An appraisal is a licensed, independent opinion of a property's market value, ordered by the lender and paid for by you, that the bank uses to decide how much it will lend against the place. It is the number that quietly makes or breaks a purchase or a refinance, because the loan is sized against the lower of the appraised value and the price you agreed to pay.
In practice
A licensed appraiser visits the property, measures it, notes its condition, then pulls three to six recently sold homes nearby that match it on bedrooms, bathrooms, square footage, and age. They adjust each comparable up or down for differences (a finished basement, an extra bathroom, a worse location) and land on a single value. Say you agree to buy a duplex for $340,000 and put 25% down, expecting a $255,000 loan. If the appraisal comes back at $325,000, the lender sizes the loan against that lower number, so 75% of $325,000 is $243,750, not $255,000.
That $11,250 gap does not disappear. You either bring it in cash on top of your down payment, renegotiate the price down toward the appraised value, or walk if your contract lets you. On a refinance the math bites the same way: if you owe $200,000 and want to refi at 75% loan-to-value, an appraisal of $325,000 supports a $243,750 loan, but an appraisal of $300,000 supports only $225,000, which can be the difference between pulling cash out and barely covering closing costs.
Why it matters to a small landlord
The appraisal is the one number in a deal you have the least control over, and it gates both ends of ownership. On the way in, a low appraisal can blow up your deal analysis if you have to add cash, because every extra dollar out of pocket drags down your cash-on-cash return. On the way to a refinance, the appraised value sets your loan-to-value ceiling and decides whether a buy-rehab-rent plan actually recycles your capital. The defense is to underwrite conservatively and keep an appraisal contingency in your offer so a low number is a renegotiation, not a forfeited deposit.
An appraisal sits next to a few terms worth holding together. It differs from a comparative market analysis, which is an agent's informal value estimate rather than a licensed lender-ordered opinion, and from an after-repair value, which estimates what a place will be worth once renovations are done rather than its condition today. The clause that protects you when an appraisal lands low is the appraisal contingency. Treat all three as the same conversation about who decides what a property is worth, and what happens when they disagree.