Property Tax Proration at Closing: A Yorkville, IL Guide

Why Does Your Illinois Closing Statement Show an Estimated Property Tax Credit?

Illinois counties, including Kendall and Kane, bill property taxes a full year behind. That means the tax bill for 2026 doesn’t get mailed until 2027, so at closing there’s no final number to work from yet. Instead, your closing statement uses an estimated credit, usually the seller crediting the buyer 100% to 110% of the most recent full-year bill, prorated for the days the seller owned the home that year. It’s not a mistake. It’s how every closing in Illinois has to work.

By Kealan O’Neil | September 18, 2026

If you’ve looked at a closing statement for a Yorkville, Oswego, or Montgomery home and wondered why the property tax line doesn’t match anything you’ve seen on the county treasurer‘s website, you’re not missing something. The number on your statement is an educated estimate, and understanding why takes about five minutes.

Illinois Bills Property Taxes a Year Behind

Most states send you a tax bill for the year you’re currently living in. Illinois doesn’t work that way. The tax bill you receive in 2026 covers 2025, and the bill you receive in 2027 will cover 2026. Property taxes here are always paid in arrears, a full year behind the year they were assessed.

The practical effect: at the moment you close on a home, the actual tax bill for the current year hasn’t been calculated yet. It won’t exist until roughly a year later, after the county assessor finalizes values, local taxing bodies set their levies, and the county clerk calculates the rate. Nobody at the closing table, not the title company, not the attorneys, not you, can look up the real number, because it doesn’t exist yet.

That’s the gap the proration credit is built to fill.

How the Proration Credit Actually Gets Calculated

Since the real bill isn’t available, Illinois closings estimate it using the most recent known bill and a percentage that accounts for typical year-over-year increases. In the Chicago area, including Kendall and Kane County, the most common approach looks like this:

• Start with the most recent full-year tax bill for the property.
• Multiply it by an agreed percentage, commonly 100% to 110%, sometimes as high as 125% in a market where values are climbing quickly, to build in a cushion for the fact that the real bill will likely be higher than last year’s.
• Prorate that estimated amount for the number of days the seller owned the home during the current tax year.
• The seller credits that amount to the buyer at closing, since the buyer will eventually be the one who has to pay the actual bill when it arrives.

The exact percentage is a negotiated term in your contract, not a fixed law, which is why you’ll sometimes see it listed as “TBD” and settled during attorney review. A seller who wants to minimize their credit will push for 100%. A buyer’s attorney, especially in a year where assessed values are rising fast, may push for 110% or higher to protect their client from being underpaid.

Here’s a simplified example on a $400,000 Yorkville home with a $9,000 prior-year tax bill, closing on July 1:

• $9,000 × 105% = $9,450 estimated annual bill
• $9,450 ÷ 365 days = about $25.89 per day
• Seller owned the home for roughly 182 days that year: 182 × $25.89 = about $4,712 credited to the buyer at closing

That $4,712 shows up as a seller-paid credit on the closing statement. It’s not a fee. It’s money the seller owes for the months they lived in the home before the real bill catches up to them.

Why This Number Can Surprise People Later

The estimate is built to be close, not exact. Once the actual bill arrives the following year, in Cook County and the collar counties alike, it’s not unusual for it to land above or below the estimate, especially after a sale, when a higher purchase price can influence the reassessed value in future years. That’s the mechanism behind the “sticker shock” stories you may have seen out of suburban Chicago, where a buyer’s real bill came in well above what the closing estimate suggested.

A few things worth knowing before you’re at the closing table:

• The proration credit is not a guarantee of your future tax bill. It’s a starting estimate based on the seller’s history in the home, not a forecast of what the county will assess going forward.
• Some deals include a reproration clause. Buyer and seller agree that once the real bill for the year of sale is issued, they’ll true up the difference, either direction, based on the actual number instead of the estimate.
• Exemptions reset with ownership. If the seller had a homestead exemption applied, that exemption doesn’t automatically transfer. You’ll want to confirm you’ve filed for your own exemptions so future bills reflect them.

This is exactly the kind of detail I walk buyers and sellers through before we ever get to the closing table, because the percentage you negotiate in your contract has a real dollar impact on both sides.

Property Tax Proration Isn’t the Same as SSA Taxes or Transfer Tax

If you’ve been researching Fox Valley closing costs, you’ve probably run into two other tax terms and it’s easy to lump all three together. They’re not the same thing:

• Property tax proration is the general county tax credit described above, and it applies to every residential closing in Illinois, resale or new construction.
• SSA and backup SSA taxes are a special assessment that only applies in certain new construction subdivisions in Yorkville and Montgomery, layered on top of your regular property tax bill to pay off infrastructure bonds.
• Municipal, county, and state transfer tax is a one-time tax based on your sale price, paid at closing, and the municipal portion varies by town, Yorkville and Oswego each set their own rate.

Knowing which line item is which makes your closing statement a lot less intimidating, and it’s worth reviewing all three if you’re comparing a new construction purchase against a resale home.

Common Questions About Property Tax Proration in the Fox Valley

Here’s what buyers and sellers in Yorkville, Oswego, and Montgomery ask most often once they see the proration credit on a closing statement.

The Bottom Line

The number on your closing statement isn’t wrong, it’s an estimate built into how Illinois bills property taxes a year behind. Understanding the formula, and negotiating the right percentage for your situation, protects you whether you’re the one giving the credit or the one receiving it.

If you’re buying or selling in Yorkville, Oswego, Montgomery, or anywhere in the Fox Valley and want to know what a realistic proration number looks like for your specific home, I’m happy to walk through it with you. Call or text Kealan at 630-425-8815.

About Kealan O’Neil
Kealan O’Neil is the Designated Managing Broker and founder of O’Neil Property Group, an independent real estate brokerage serving Yorkville, Oswego, Montgomery, and the surrounding Kendall and Kane County communities of the Fox Valley. He and his team walk buyers and sellers through the Illinois closing process daily, and he also self-manages a local rental portfolio, so he approaches every tax and closing question as both a broker and an investor. Call or text Kealan at 630-425-8815.

This post is general information about real estate in the Fox Valley, not legal, tax, or financial advice. Real estate laws, tax rules, and municipal ordinances change, and how they apply depends on your specific situation. Talk with a licensed attorney, CPA, or lender before making decisions about a purchase, sale, or tax matter. O’Neil Property Group is a licensed Illinois real estate brokerage.