A sweeping trend of lower home values has decreased the property tax bills for 70 percent of Westport homeowners this year, despite increases in town spending and the tax rate, according to data released last week by town Assessor Paul Friia.

Approximately 3,900 taxpayers, or 45 percent of homeowners, will see their tax bills decrease by 10 percent or less. About 2,000, or 23 percent of Westport homes, will receive tax bills between 10 and 20 percent less than last year, while about 200, or 2 percent of homes, will see a tax decrease of more than 20 percent.

Conversely, tax bills will increase by 10 percent or less for 20 percent or about 1,800 Westport homes, while 6 percent, or about 500 taxpayers, will see their property taxes go up between 10 and 20 percent. About 350 homes, or 4 percent, will face an increase of more than 20 percent.

The tax rate "is the one component that adjusts your taxes every year," Friia said. "In the revaluation year, there really is the tax rate and the new assessments. In this year, you have to look at both parts of that equation to come up with what your taxes are actually going to be."

With revaluation, the total value of the town's taxable property fell 12.5 percent.

After revaluations, tax rates typically change to reflect new total property value.

When total property value rises, the tax rate typically declines to produce a similar amount of tax revenue. When the total property value declines, the tax rate typically must rise to produce similar revenue.

Friia's calculations factor in the impact of the revaluation, plus a 2.95 percent increase in the town budget.

The new 2011-2012 tax rate of 17.43 mills -- $17.43 per $1,000 of assessed value -- is 17 percent higher than last year's rate of 14.85 mills. The finance board approved a revenue hike of 2.95 percent that funds the budget increase, unbudgeted expenditures and a $3 million earmark for the town employees' Other Post-Employment Benefits fund.

The 2.95 percent increase is based on a "break-even" or adjusted tax rate of 16.93 mills that would keep town receipts constant following the revaluation. The adjusted rate would raise the tax rate by 14 percent to offset the 12.5 percent revenue decrease caused by the revaluation.

Homeowners who saw their bills increase will assume a larger proportion of the tax burden, a shift attributable to the new home assessment values produced by the revaluation.

"Any real estate accounts -- residential or commercial -- that have gone up are going to pick up the (tax rate) increase, as well as motor vehicle and personal property," Friia added.

Motor vehicles and personal property are assessed annually, but Friia said their value generally does not decrease as much as the tax rate increased this year. As a result, he said that most motor vehicle and personal property tax bills will probably be higher this year.

Friia's data reflect the impact of the new tax rate for approximately 8,700 single-family homes, which constitute almost 100 percent of the town's single-family housing stock. That total does not include about 200 residential properties that have undergone significant building work during the last year. The assessor's data also do not comprise commercial properties or vacant land.

Condominiums generally held their values better than single-family homes, according to Friia. About 300 taxpayers, or 57 percent of condo owners, have higher tax bills this year; the remaining 43 percent, approximately 230 condo owners, have lower bills.

Tim Eckert, a resident of northwest Westport, said both his real estate and motor vehicle tax bills have increased this year. He reported that the tax bill for the home he shares with his wife increased 11 percent, despite a 5.5 percent decrease in its assessed value following last year's revaluation. In addition, he said the tax due on his two cars increased by 15 percent and 18 percent.

"Call us three-time losers," he said. "When you look at it on a year-to-year basis, that's a substantial bite."

Eckert added that he would like to see town officials improve their communication with residents about the revaluation and the tax rate.

"The town does not have a clear voice, in that basically any department head can communicate," he said. "That can lead to confusion."

Property tax bills are paid quarterly in Westport. The first installment can be paid without a penalty by Aug. 1.