Homeowners could be surprised by the valuation put on their homes when they receive letters from Revenue this week.
As authorities prepare to collect the new Property Tax, Revenue is to begin distributing tax forms to 1.8 million householders nationwide.
Yesterday, Revenue published its online guide to property values based on the average price in the area and the age of the house.
Many observers have said some of the guide's estimates are actually below market value.
Managing Director of MyHome.ie, Angela Keegan said that could depress the market.
Ms Keegan said: "I know I looked at some homes where I would be fairly familiar with their values, and most certainly the Revenue calculation is less.
"I think that really shouldn't surprise us, because they have gone with the electoral district level, and within the electoral zones there is such a wide variation of homes in the semi-detached or detached category."