The base year
Allegheny County doesn't update assessments every year. It uses what is called a base year. In the county's words, "Our current base year is 2012 with an effective date of value of January 1, 2012," and that base year "was used for tax year 2013 and all tax years since."
So the assessed value on a record is the county's estimate of what the property was worth on January 1, 2012. A house that has doubled in price since then still carries its 2012 number. The county is plain about it: assessed values on its site "do not reflect current year market values."
When an assessment can change
Between reassessments, the county says it can only change a property's value for a short list of reasons:
- Omissions
- Mathematical or clerical errors
- Physical changes such as demolitions, subdivisions and building permits
- An interim assessment on new construction or major improvements, which a school district or municipality sometimes requests
An appeal can change it as well, and so can a catastrophic loss such as a fire, if the owner applies within six months.
The common level ratio
Because base-year values drift further from real prices every year, the state publishes a number that connects the two. It is called the common level ratio, and it describes how assessments in a county compare with recent sale prices.
The county says the ratio for the 2027 tax year is 49.3%. Put simply, assessments countywide now run at about half of what properties sell for.
The ratio matters most in an appeal. The appeals board works out what the property is worth today, then multiplies by the ratio to get the assessment. A house worth $300,000 today would be assessed at $147,900 using 49.3%. If your current assessment is well above your home's value times the ratio, an appeal may lower it. If it is below, an appeal by your school district or municipality could raise it.
The ratio has been falling as prices rise. The state's figures were 54.5%, then 52.7%, then 50.14%, before the current 49.3%.
A reassessment is coming
On August 17, 2026, a Court of Common Pleas judge ordered the county to carry out a new countywide reassessment to replace the 2012 values. According to the county's announcement, it must start the reassessment by 2027 and complete it within five years. The judge also directed regular countywide reassessments every five years after that.
Until new values take effect, the 2012 base year still applies, and so does everything above.
What to use instead
For a sense of what a property is worth now, look at what it and its neighbors sold for. Parcel Finder shows each property's recorded sales next to its assessment, along with the comparable sales the county used. The municipality pages give the median sale price for each community over the past year.
Sources
- Allegheny County: Property Assessments, for the base year and the reasons a value can change
- Allegheny County: Board of Property Assessment Appeals and Review, for the 2027 ratio
- Pennsylvania State Tax Equalization Board: common level ratios, for earlier years
- Allegheny County bulletin, August 17, 2026, for the court order