Secretary of State Charlie Summers and his wife earned an average of $95,761 a year over the past seven years, and paid 8.6 percent of that in federal income taxes.

State Sen. Cynthia Dill, D-Cape Elizabeth, and her husband earned an average of $56,853 a year over the past seven years, and paid 4 percent of that in federal income taxes.

Former Gov. Angus King and his wife earned an average of $568,868 a year, and paid 15.3 percent of that in federal income taxes.

The Portland Press Herald analyzed the federal tax returns of Maine’s top three U.S. Senate candidates Tuesday. The campaigns released the documents over the course of the day Monday, starting with King at noon and ending with Dill shortly after 10 p.m.

Dill, who proposed the public disclosure last week in a challenge to her rivals, released 10 years of filings. Summers released eight years of returns and King released seven. The tax returns contained no surprises about any of the candidates.

King’s filings confirm that he is by far the wealthiest of the three candidates, mostly because of the sale of his energy conservation business in 1994.

Much of King’s and Herman’s income is from investments, which is taxed at a lower rate than earned income, but they nevertheless paid a higher effective tax rate than Summers or Dill.

King and his wife also reported much larger contributions to charity — 13.4 percent of adjusted gross income over the seven-year period.

Summers and his wife are in the higher middle-income range, at least by Maine standards. Ruth Summers is vice chairwoman of the Maine Republican Party and a Maine Senate candidate in Scarborough.

Nearly all of their income came from salaries over the past seven years. They used typical deductions and tax credits to reduce tax liability. They reported charitable contributions of hundreds of dollars each year, amounting to 0.5 percent of their adjusted gross income.

Dill and her husband are solidly middle income. She is a self-employed lawyer and he is a teacher. They use common tax deductions and report losses on a rental property in Cape Elizabeth, both of which reduce income tax liability. From 2006 to 2008, the couple had no taxable income but did pay self-employment tax on business earnings from Dill’s law practice.

Dill and her husband reported charitable contributions totaling 2.5 percent of their adjusted gross income over the seven-year period.

Tax returns might be useful for some voters, but disclosure serves mostly to ensure that candidates are following the rules, said Steven Colburn, associate professor of accounting at the University of Maine.

“I don’t know if it’s a valid thing to criticize people for the rate of tax they pay if they are applying the tax laws fairly,” he said. “I think there are a lot of voters out there who don’t know what their tax rate is.”

While the candidates’ returns were predictable, the issue of whether candidates should release them took on some of the overtones of class politics that have characterized the presidential election.

In the presidential race, Democrats have hammered away at Republican Mitt Romney for not releasing past years’ tax returns. Romney has so far released the past two years, along with a letter from his accountant saying he did not pay less than 13 percent of his adjusted gross income in taxes during the past 20 years.

In 2011, Romney and his wife earned $13.7 million and paid 14.1 percent of that in federal income tax.

President Barack Obama and his wife, meanwhile, earned $790,000 and paid 20.5 percent in federal income taxes.

Romney pays a lower effective tax rate in part because more of his income comes from investments, and those capital gains are taxed at a lower rate than earned income.

In Maine’s Senate race, Dill has criticized King as a “1 percenter” and a wealthy political insider.

Dill called on her rivals last week to release their returns to an independent third party at 5 p.m. Monday. Both Summers and Dill criticized King for not agreeing to the proposal immediately.

On Monday, King’s campaign released his returns to the media earlier in the day, forcing the Dill and Summers campaigns to catch up. Neither produced their tax returns until Monday night, too late to be analyzed in detail for an article published Tuesday.

Republicans and the Summers campaign criticized King on Tuesday for providing a summary of his returns that highlighted a 22.2 percent effective tax rate over seven years. They accused King of trying to overstate his tax payments.

King’s summary based his tax rate on taxable income — the amount after credits and deductions — rather than adjusted gross income.

Tax experts said Tuesday that both ways of calculating tax rates are valid, and some prefer using taxable income because that is how the tax is calculated. The key, they said, is being consistent when comparing them.

Based on taxable income, Summers paid a 12.4 tax rate and Dill paid a 15.7 percent tax rate over the seven-year period.

John Richardson — 791-6324

jrichardson@pressherald.com