If you own a mansion in Calgary, there's good news and bad news today.

The good news is you're likely getting a break on your property taxes.

The bad news is that's because the value of your home likely dropped a lot faster than everyone else's.

The City of Calgary released its 2016 assessment Tuesday and, overall, the value of residential properties declined by one per cent from last year.

But the median value of single-family homes actually increased by about one per cent — to $480,000, up from $475,000 last year — because of what chief city assessor Nelson Karpa described as an uneven change in the real-estate market.

"In a nutshell, we saw the value of high-value properties drop fairly dramatically," Karpa said.

Moderately and lower-priced homes, meanwhile, stayed relatively stable.

'Magic number'

Based on the city's "revenue-neutral" system of property taxation, that means many high-end homeowners will see their property tax bills go down this year.

The system sees city council set a total amount of tax to be collected and the amount each property owner pays is then based on their individual assessment relative to the whole.

The "magic number" this year is negative one per cent.

If the value of your home declined by more than that, your share of the tax burden will go down.

If the value of your home changed by more than that amount, your share of taxes will go up.

Office space leads non-residential declines

On the non-residential side, meanwhile, the "magic number" is negative four per cent.

Karpa said the decline in non-residential property values was largely driven by commercial office space, which plunged about 12 per cent, with the biggest declines in downtown office towers, many of which have "a lot of vacancy."

"Some of the suburban offices did a little bit better," Karpa said.

Retail properties declined in value by about one per cent while industrial property values grew by about four per cent, he added.

How assessments work

Calgary's annual assessments reflect the city's estimate of what a property was worth on July 1 the year before.

So, the 2016 assessments represent estimated property values on July 1, 2015.

Assessment notices are being mailed today to property owners, telling them what their tax bills will be for 2016.

If you disagree with your assessment or think a mistake has been made or have any questions, you contact the city assessors at 403-268-2888 before March 7.

More information can be found at calgary.ca/assessment.