The total value of taxable property in Wareham plunged by more than 7 percent in the past year, due largely to a decline in residential real estate values.

The result is that, even with the town staying within the bounds of tax-limiting Proposition 2½, property owners whose assessments have not changed in the past year will see their town taxes increase by 11.7 percent.

Earlier this month, the state Department of Revenue certified Wareham’s tax rate at $10.47 per $1,000 of assessed valuation – a rate of 1.05 percent. The 2012 rate was $9.37 per $1,000 valuation – a rate of 0.94 percent.

Director of Assessment Elsa Miller explained the drop in assessed value of town property as being largely due to a 6 percent drop in the average value of a single family home.

While town assessments are not exactly in line with what individual properties would sell for on the open market, they are intended to reflect that open market value. In addition to periodic routine reassessments, using a mathematical formula for valuation, assessments are reset when a property changes hands for a price different from the assessment.

The total taxable property number is dragged down every time a home sells for less than its assessed value in three ways: That property’s assessment is reset. The basis on which similar houses are routinely reassessed declines. And, over time, owners of similar houses have a better basis on which to seek a lower assessment through the abatement process.

Not every type of property has been equally affected by the decline in value.

“Different classes – single families, multi-families -- they went down differently and some didn’t go down at all,” said Miller. “Commercial/industrial hasn’t really changed.”

The 11.7 percent increase in the tax rate is the effect of the town’s budgeting to spend 2½ percent more than in 2012, but having only $3.1 billion of property to tax, down from $3.4 billion last year.

For those confused by the numbers, think of the total amount to be raised by taxes as a pie. The pie got a little bit bigger, but the number of people sharing it went down by a lot, so everyone has to take a bigger piece. That’s a good thing if what is being shared is a pie – not so good if it’s taxes.

Proposition 2½ limits the increase in total town tax revenue to 2½ percent a year, but says nothing about the increase in an individual property owner’s tax bill.

In Wareham, where independent fire districts in Onset and Wareham separately tax property owners, those taxes are being similarly affected by the decline in property values.

Although the 7.4 percent drop in assessed value is the sharpest Wareham has seen in recent years, it is only acceleration of a trend. The value of total taxable property in town has been declining since hitting a high of 2008, shortly after Wareham Crossing opened and following several years of housing growth during what is now referred to as the nationwide “bubble” of inflated housing prices.

Since 2008, Wareham has seen a 20.7 percent drop in total property values.

When the 2013 tax figures were published last week, some residents posting on WarehamVillageSoup.com complained that the increase in tax rate violated the strictures of Proposition 2½.

“There are a lot of misconceptions on Prop. 2½,” said Board of Assessors Chair Steve Curry. “The town’s budget can only go up two and a half percent,” but the tax cap does not apply to individual homeowners.

Curry explained the purpose of Prop. 2½ in simple math terms: “Say the town’s budget is $100. The next year they can only spend $102.50.”

According to Curry the point of the law is prevent municipalities from spending excessive amounts of money, and sticking taxpayers with the bill.

“The town can’t decide to spend $20 million this year and $60 million next year, then put it on the taxpayers,” he said.

Based on the assessment for fiscal year 2013, Wareham’s “property tax levy,” or the amount the town will need to collect in revenue, is $32,630,489.

The fiscal year begins on July 1, and ends on June 30 of the following year. Every year, the Massachusetts Department of Revenue calculates the maximum amount a town is allowed to charge in personal and real property taxes for that fiscal year.