The way of calculating official property values is being overhauled and millions of homes may be worth more or less from January, news website Nu.nl said on Friday.

The new calculations are partly based on floor size rather than cubic metres and this will have an impact on some homes, supervisory agency Waarderingskamer, told the website.

Some 250 of the 352 local authority areas in the Netherlands are making the switch – the rest have already done so, Nu.nl said. ‘The way in which WOZ values were calculated was not accurate enough,’ inspector Ivo Lechner said.

WOZ values are used to calculate local authority taxes, so some households may end up paying more, or less. As well as the actual size of a property, local house prices and the sale price of comparable buildings also have a major impact.

‘It is not yet clear what the consequences are likely to be,’ Lechner said. ‘In local authority areas where the switch has been made, the impact has been limited.’