The tax bill covers a period from April 1st through March 31st.
The first installment tax bill is mailed out by the end of May and is typically due by July 1st before interest starts accruing. The first bill is an estimated bill calculated on half of the previous year's tax rate multiplied per $1,000 of the current assessed value of the property.
Before the second installment property tax bill is mailed, the Department of Revenue Administration must set the tax rate for the year. This usually takes place at the end of October. The final bill is calculated using the new tax rate multiplied per $1,000 of your property's current assessed value as of April 1st, less any payments made on the first bill.
(Property Taxes are not prorated at the town level due to inaccuracies but closing agencies typically prorate property taxes as July payment is April 1st through September 30th and December payment is October 1st through March 31st of the following year).