Some people might be surprised to find out that their taxes are negotiable — at least when it comes to real estate. Specifically, 53 percent of Texas homeowners don't know they can protest their home's property tax evaluation, according to a study by Ownwell, a service that makes homeowners' cases for them.

Put simply, since homeowners are taxed on the assessed market value of their home, an over-appraisal by the local tax office can lead to paying too much in taxes. Homeowners in this situation can lower what they owe by telling tax appraisers what they believe the real value of the home is, and the two entities will negotiate to find an acceptable number. Appraisals reflect the value of the home on January 1 of that tax year.

For most Houstonians, the appraisal is made within the Harris County Appraisal District (HCAD), and the case will be heard by the Appraisal Review Board (ARB).

Across Texas, the deadline to submit a "protest" — information about the homeowner's proposed market value of their home — is Thursday, May 15. That means Houstonians have less than two weeks to take action. Submitting the information is just a first step; later, they'll have to present evidence in an informal meeting, in a hearing, or by affidavit.

What homeowners don't know
There are a few reasons homeowners may not be aware protesting is an option. Hopefully, their realtor explained the process, but they're technically not required to do so. With all the mental load of buying a home, especially if it's months between closing and January 1, it's possible the homeowner heard their options without understanding, or even simply forgot.

There are other ways to find out, but the most official path to knowledge requires reading mail from the county in detail.

Ideally, homeowners should receive a written Notice of Appraised Value in the mail before the deadline. In Harris County, the mailer comes with a mostly blank copy of the Property Owner's Notice of Protest (Form 50-132), which they can fill out and submit. It also comes with some instructions on how to submit the form and expected timelines.

However, sometimes mail delays, administrative accidents, or other mishaps mean a homeowner does not receive their notice in the mail. Homeowners can search for their notice online even if they did not receive it, and they should. Missing the deadline doesn't mean the mistake can never be fixed, but it adds confusing extra steps.

Ownwell found that more than half of Texas homeowners were "shocked" at their last property tax bill. More than 70 percent had not even sufficiently budgeted for the expense, and they had little reason to, since one in three of them felt their assessment was higher than it should be.

Additionally, statewide:

• 75 percent of homeowners reported a notable increase in taxes since moving in
• 72 percent worry about further significant increases
• More than 80 percent feel their housing costs are too expensive

What hiring a service means
There's a lot of money on the table, and there's little to no risk in protesting. If the appraisal review board doesn't agree after hearing your case, there is no penalty for an unsuccessful protest.

Ownwell, specifically, is a popular choice because its representatives work on a contingency fee. In other words, the service doesn't cost anything until they've earned money back. In many Houston ZIP code, the service costs 25 percent of the amount saved. If they don't save anything, the service is free.

It is common for tax protest services to have extremely high success rates. Ownwell claims a success rate of 86 percent. Tax Cutter claims a success rate of 96 percent and offers a 25 percent contingency, or options to keep all the savings for an upfront fee. Gill, Denson & Company also works on a 35 percent contingency, with discounts for more properties, and claims a success rate of "more than 80" percent. There are tons of options out there, but Ownwell does have a very friendly user experience and strong marketing.

DIY protests
If homeowners feel ready to take on the responsibility, they can find all this information online — but they will need to be diligent about timelines, details, and maintaining the proper contacts.

Common advice is to talk to your realtor about the process and ask for "comps," data on comparable properties nearby and their value. A large portion of a property's value is based on the land and its location, so sometimes it helps if neighbors all use the same service. However, be sure not to base too much on your neighbor, says TaxProtestMap. There are a lot of other variables from house to house.

There are endless online resources, but combing through the same general information over and over can be exhausting, especially when there is an uncommon detail to work around.

For example, there are separate forms for properties with particularly egregious over-appraisals with and without homestead exemptions, late protests, and more. These don't come up in most how-to guides, and what little information is available tends to be rephrased or copied ad nauseam, rather than presented in new ways that might actually clear up confusion.

Why first-time homebuyers have a leg up
This can all be overwhelming, but first-time homebuyers actually have an advantage if they're well informed, and especially if they closed on their house toward the end of the year.

The first year someone buys a house is often the most straightforward, because they have hard evidence of how much their house was really worth on the market: whatever they paid for it. It'd be very hard for appraisers to argue that a house was really worth $500,000 if it only sold for $350,000. Wouldn't the seller hold out for more if buyers were willing to pay more?

The closer the house sold to January 1, the less time any surrounding land had to appreciate in value by that appraisal date. Plus, homeowner improvements do factor in, so the less time, the better for all but the most expeditious homeowners.

For example, if you close on a house on December 18, there are only two weeks between then and the following year's appraisal. Most homeowners won't have implemented tens of thousands of dollars of improvements by then, and it's easy to argue the house is worth what you paid.

The bottom line
No matter what, just knowing property taxes can be protested is a huge step in saving homeowners money. Whether they use a service or learn how to protest on their own, homeowners' benefits usually far outweigh the effort of learning how to protest. And the best part: learning now makes next year way easier.