Calgary homes lost about four per cent of their value in the past year while non-residential properties went down about six per cent, according to the city's latest assessment.

The median Calgary house is now worth $460,000, according to the city's estimates, down from $480,000 last year.

The median condominium value is now pegged at $270,000, down from $280,000 in the 2016 estimate.

The annual re-evaluation of property values is used to determine property tax bills. The city will mail out roughly half a million assessment notices this week. Property owners who disagree with their assessments have two months to appeal for a change.

Non-residential properties as a whole saw an even greater decline than homes but acting city assessor Harvey Fairfield noted the changes were not evenly distributed.

Retail properties actually saw a slight increase in total value, while industrial properties were roughly flat, he said.

But properties in the office category were down by 16 per cent, a major swing Fairfield said was driven largely by growing vacancy rates in downtown office buildings.

What does this mean for your tax bill?

Individual property taxes are calculated by multiplying the tax rate by the assessed value of a property.

Calgary's "revenue neutral" method of calculation means the total dollar value of the municipal tax haul is kept the same from year to year, prior to any increases or decreases approved by city council, and the tax rate is adjusted based on the overall assessment.

That means your own tax bill depends on how your property value changes relative to the overall change across the city.

So this year, if your home dropped in value by four per cent, your bill won't change. If it dropped by more than that, you'll pay less in tax. If it dropped by less than that or increased in value, you'll pay more in tax.

The same goes for non-residential properties, but the magic number is six per cent.

$15M to help struggling businesses

This approach to taxation means many business owners outside of downtown will face big hikes in their non-residential tax bills this year, due to their relative position to the overall assessment. Many downtown office buildings, by the same mechanism, will see hefty reductions in their tax bills.

In November, city council earmarked $15 million to help struggling businesses but it's not yet clear how that money will be administered.

The annual assessments are based on the city's estimate of what a property was worth on July 1 of the previous year. So this year's assessments reflect property values on July 1, 2016.

If you think your assessment is inaccurate and want to ask for a change or file a complaint, you must do so by March 6.

About 4,500 complaints were filed last year.