You find a home in Round Rock. The listing sheet shows a tax bill you can live with, so you build your monthly payment around it. A year after closing, the county mails a new appraisal, and the number on your escrow statement doesn't match the one you underwrote at contract. Nothing went wrong. The system worked exactly as designed.
Here is the part almost nobody explains before the offer goes in: the tax figure attached to a Round Rock listing describes what it costs the current owner to keep that house, not what it will cost you. Texas caps how fast a homesteaded property's taxable value can rise each year, but that cap belongs to the person holding the exemption, not to the walls and the roof. When ownership changes, the cap doesn't travel with the deed. The Williamson Central Appraisal District resets the property toward its market value on the next January 1, and the gap between the old number and the new one can be the difference between a tax line you planned for and one that blows a hole in your first-year budget.
The Cap Follows the Owner, Not the House
State law limits the annual increase in a homesteaded property's assessed value to 10 percent, no matter how much the market value climbs in a given year. That protection has done real work in Williamson County over the past several years. Austin-area values ran up sharply between 2020 and 2023 and have since cooled in many neighborhoods, but a longtime owner who has held the same homestead exemption the whole time never absorbed the full swing. Their assessed value crept up in capped 10 percent steps while the market moved in bigger jumps, so by the time they list the house, their taxable value can sit meaningfully below what a buyer would actually pay for it today.
That's the number printed on the listing flyer. It's accurate for the seller. It tells you almost nothing about what you're about to inherit.
The tax bill on the listing sheet describes what it costs the current owner to keep the house. It says nothing about what it will cost you to own it.
What Actually Happens the Day the Sale Closes
A homestead exemption requires the owner to occupy the property as a primary residence as of January 1 of the tax year being claimed. Once a seller no longer owns and occupies the home, that exemption falls off, and with it the cap that had been holding the assessed value down.
Say you close on a Round Rock home this fall. You become the owner of record before the end of 2026, but the tax year that matters for your first bill is the one that starts January 1, 2027. If you're occupying the home as your primary residence at that point, you can file your own homestead exemption using Form 50-114 with the appraisal district, with an April 30, 2027 deadline and late filings still accepted through January 31, 2028. Until that exemption is on file, the property sits in a non-homestead status for appraisal purposes, and non-homestead properties carry no cap at all. The appraisal district can move straight to market value.
Williamson Central Appraisal District mails its Notice of Appraised Value each spring, typically in April, reflecting the ownership and occupancy status as of the preceding January 1. Your first full tax bill as the new owner lands around October 2027, due by January 31, 2028. That's the bill built on the fresh appraisal, not the seller's capped number. If the home has changed hands only once or twice in the past decade, the difference between those two figures can be substantial.
The Exemption Increase Helps. It Doesn't Cancel the Reset.
Texas voters approved a further increase to the school district homestead exemption in November 2025, raising it from $100,000 to $140,000 of taxable value on top of the earlier 2023 increase. Once your own exemption is filed, that larger exemption reduces the taxable base on the largest slice of a typical Williamson County bill, the school district portion, which usually runs 45 to 55 percent of the total.
That's a real benefit, and it's worth claiming as soon as you're eligible. But it solves a different problem than the one buyers usually assume it solves. The exemption reduces your taxable value once you have your own homestead status in place. The cap limits how fast that value can rise year over year after that. Neither one softens the initial jump from the seller's old, capped assessed value to your fresh, market-based assessment. A new owner gets the benefit of the larger exemption starting from a higher base, not a discount on the reset itself.
Before You Write the Offer
- Search the property on the appraisal district's public site and look at both the market value and the assessed value, not just the tax line on the listing flyer.
- Check whether the seller currently holds a homestead exemption. If they do, treat the gap between market value and assessed value as roughly the size of the increase headed your way.
- Ask your lender to escrow against the market-value estimate rather than the seller's trailing tax bill, so you're not short when the first reassessment lands.
- If the home sits inside a Municipal Utility District, add that district's rate on top of the base city, county, and school rates before comparing it to a listing outside a MUD.
- File your own homestead exemption the spring after you occupy the home as your primary residence, so your cap and your larger exemption both start on schedule instead of a year late.
Location Inside Round Rock Still Changes the Math
Round Rock straddles Williamson and Travis counties and several overlapping taxing entities, and the effective rate a given parcel actually pays depends on which school district, city, county, and special district reach it. Combined effective rates across Williamson County generally run 1.9 to 2.4 percent of appraised value depending on that mix, and newer subdivisions built inside a MUD or PID typically carry an additional 0.3 to 0.7 percentage points on top of the base rate. That overlay matters most in the newer master-planned neighborhoods where much of Round Rock's recent construction sits, since older, already-platted parts of town were largely built before those districts existed.
Even within city limits, the ZIP code you land in shifts the number:
ZIP Code | Median Effective Rate | What Typically Drives the Difference |
|---|---|---|
78664 | 1.35% | Older-platted areas, fewer MUD overlaps |
78665 | 1.49% | Newer subdivisions, more MUD and PID layering |
The City of Round Rock's own portion is a smaller piece of that total. Its adopted rate for fiscal year 2025-2026 is 37.2 cents per $100 of assessed value, layered onto the county, school, and any MUD rates that also reach the parcel. The median home value on the city's 2025 tax roll sits at $395,240, which gives a sense of scale for how quickly the city portion alone moves once you multiply it against a market-reset assessed value instead of a capped one.
The Number That Should Anchor Your Budget
A national rate comparison or a portal's estimated payment calculator will price the house as it's taxed today, under the current owner's exemption and cap history. That's not the number that determines your monthly payment a year from now. The number that matters is the one the appraisal district will assign to the property once your ownership and occupancy reset the clock, and that number is knowable before you write an offer if you pull the public appraisal record instead of relying on the tax line printed on the flyer.
This is the kind of detail that's easy to miss from a listing page and easy to catch with someone who works Round Rock closings regularly. If you're comparing homes and want a second set of eyes on what a specific property's tax exposure will actually look like after closing, JBGoodwin Realtors can walk through the appraisal history with you before you're locked into a contract. Contact us and we'll help you build your offer around the number you'll actually pay.
A Short FAQ
Does the 10 percent cap ever apply to me right away as a new buyer? No. The cap only applies once you hold your own homestead exemption, which requires owning and occupying the home as your primary residence as of January 1 of the tax year you're claiming it for.
What if the seller has an over-65 or disabled exemption instead of a standard homestead exemption? Those exemptions carry their own freeze on the school tax portion, tied to the qualifying owner. That freeze ends when the home sells, and a new owner starts from the current market value, not the frozen number the previous owner enjoyed.
Is this unique to Round Rock? The cap and exemption rules are set by the state, so they apply anywhere in Texas. What changes from one Round Rock block to the next is the total rate layered on top, driven by which school district, MUD, and PID reach that specific parcel.
