Cook County tax proration gives a buyer a closing credit for the seller’s agreed share of unpaid property taxes. That credit reduces the cash needed at settlement. It does not set the eventual bill or automatically put money aside to pay it.

For an existing-home purchase, gather the signed contract and amendments, latest full-year tax bill, installment payment history, exemption record and draft settlement statement. If financing includes tax escrow, add the lender’s initial escrow statement.

Why the seller gives a property-tax credit

Illinois property taxes are paid in arrears: taxes for one calendar year are generally paid the following year. A seller can therefore leave behind taxes attributable to time they owned the home even when no payment is overdue. The Illinois Department of Revenue’s December 2025 publication describes current-year prorated taxes being offset against the sale price at closing.

The seller property tax credit reduces both what the buyer must bring to settlement and the seller’s proceeds. The buyer then has to fund the later payments. If you are planning a home sale, include this adjustment when estimating the cash available for your next purchase.

Ask the settlement agent to organize the calculation by tax year, rather than the date a bill arrives. Separate unpaid prior-year taxes from the closing year’s proration, and account for installments already paid so the same obligation is not counted twice.

What 105% or 110% proration means

Those percentages are contract assumptions, not a Cook County guarantee or mandatory rate. Paragraph 12(a) of the Multi-Board 8.0 contract, reproduced in this training packet, leaves the percentage blank and uses the most recent ascertainable full-year bill.

A 110% calculation starts with 1.10 times that bill; 105% starts with 1.05 times it. The agreed ownership period then determines the seller’s share. Neither calculation establishes the actual next bill.

Have the settlement agent show you the base bill, percentage, dates, day-count convention and payments deducted. You cannot evaluate the percentage without knowing its starting amount. Also confirm whether the calculation is final or can be revisited.

Example: a $5,454.79 credit with no automatic reserve

Hypothetical resale: Closing occurs June 30, 2026. The parties allocate January 1 through June 30—181 days—to the seller, using actual days over 365. They agree to a $10,000 annual base and 110% proration. Earlier tax years are fully settled separately; no payments have been made toward the closing year. There is no mortgage tax escrow or separate tax holdback.

The closing-year credit is:

$10,000 × 1.10 × 181 ÷ 365 = $5,454.79

The buyer keeps $5,454.79 that otherwise would have gone to closing. It becomes a tax reserve only if the buyer sets it aside. Spending that cash leaves that portion of the future bill unfunded.

At 105%, the same assumptions produce a $5,206.85 credit. Now suppose the actual annual tax later totals $12,000. Applying the same ownership fraction gives a seller-period amount of $5,950.68, or $495.89 more than the 110% credit. That difference is illustrative; it does not create an automatic right to reimbursement. The buyer’s own ownership period also needs funding, because the seller’s credit was never intended to cover the entire year.

With lender escrow, check the separate deposit. The CFPB explains that an initial escrow deposit starts that account. Its Closing Disclosure rules separately identify escrow funding and adjustments for unpaid seller taxes. A credit on one line does not prove an equal deposit on another.

Keep this distinction in your homebuying budget: the cash needed to close and the cash needed after closing are separate amounts to plan for.

Check the seller’s exemptions by tax year

The seller’s exemptions can make the base bill a poor guide to your future costs. The Assessor’s March 11, 2026 announcement explains that exemptions reduce taxable value and directs owners to their property’s exemption history.

Check which benefits reduced the seller’s bill, then ask the assessor which you qualify for and for which tax year. Schaumburg Township’s April 2026 guidance illustrates why the year matters: applications being handled in 2026 concerned tax year 2025, with different documentation for homeowner, senior and Senior Freeze benefits.

Distinguish lawful exemptions for the year being divided from savings you can expect during future ownership. Multi-Board 8.0 requires the seller to preserve qualifying exemptions used in the calculation and excludes exemptions the seller cannot lawfully claim. Review that contract provision alongside your signed amendments.

For budgeting, request a separate estimate using your expected eligibility. Do not assume every seller benefit disappears immediately or continues indefinitely. The resulting ownership cost belongs in your assessment of housing affordability, regardless of the closing credit.

Establish whether the parties can reprorate

Reproration means recalculating the parties’ shares after better tax information becomes available. Under unmodified Multi-Board 8.0, general tax prorations are final at closing except for its improvement provision or another written agreement.

Have your Illinois real estate attorney review the signed terms and any proposed tax reproration agreement. Ask the attorney to confirm that the agreement identifies:

• The tax years and bills covered.
• How exemptions, payments and later corrections will be treated.
• Who provides the bill and calculation, and by what deadline.
• When either party must pay an adjustment.
• Whether funds will be held, who holds them and how they are released.

A final proration gives the parties certainty about the closing adjustment while leaving estimation risk. Reproration allows them to reconcile their shares later but requires follow-through. The agreement itself does not show that cash is being held.

New construction and improvements need separate attention. Paragraph 12(b) provides escrow and later proration where a property has not been taxed for a full year as currently improved. Do not apply the resale example to a land-only or partially improved tax history.

Who pays the bill after closing?

In the resale arrangement described here, the buyer arranges payment of the later bill, directly or through the mortgage servicer. Check the settlement documents for any tax payment or holdback assigned to someone else. Seeking reimbursement from the seller is separate from making sure the county receives payment.

Cook County’s August 14, 2026 mortgage-payment guidance tells owners to verify payment even when a lender handles taxes. Confirm the property index number, or PIN, the installment amount and its due date; then check that payment posted correctly.

Before closing, you should be able to point to the credit calculation, identify where payment funds will come from, name who will pay each outstanding installment and locate any deadline for reproration. Keep those records together until the relevant bills and any agreed adjustments are settled.