The income tax initiative, I-1098, would bring in more than twice as much money as proponents have said, according to a new analysis by the governor's budget office office.

Proponents of the high-earner income tax had estimated it would bring in about $1 billion annually. But the governor's budget office projects the tax would generate about $11.6 billion between 2012 and 2016.

I-1098, backed by a coalition including labor, health-care and education groups, would create a 5 percent tax rate on annual income above $200,000 for individuals and $400,000 for couples, and a 9 percent tax rate on income above $500,000 for individuals and on income above $1 million for couples. It also would cut the state property tax by 20 percent and increase the business-and-occupation tax credit for small businesses to $4,800 from $420 per year. Sponsors say the new tax revenue would help pay for education and health-care programs.

The budget office projects about $1.6 billion would be available for the next two-year budget if voters approve the measure, which could help the state solve a shortfall projected at around $3 billion.

After the first year, the tax is expected to generate more than $2 billion annually.