Property tax assessments are calculated based on the mill rate set by your town or county government. A mill is 1/1000th of a currency unit. The tax assessment is obtained by dividing the assessed value of your property by 1000 and multiplying that number by the mill rate in your locale.
One mill is one-tenth of a cent. The mill rate determines property tax. A 40 mill tax is a 4 cent tax on each one dollar of assessed property value. A 200,000 home assessed at 100,000 with a 40 mill rate is taxed at $4,000.