The property tax payable annually is computed based on a percentage of the annual value of the property. The annual value is the estimated annual rent that your property can fetch, regardless of whether you are able to rent it out or not.
If you own and occupy the property, the tax rate is 4% of the annual assessed value. If your property is rented out, the tax is currently 10% of the annual assessed value of the property.
To read more about property tax, visit the IRAS website