Con Ed electricity rates are heading up about 2.5 percent next month — a smaller increase than originally expected.

Monthly bills will rise $2.26, to $92.78, for typical Big Apple apartment dwellers who use 300 kilowatt hours, under the plan approved yesterday by the state Public Service Commission.

That’s less than the 3.7 percent increase called for in a three-year Con Ed rate plan approved by the commission in 2010. The hike is smaller because Con Ed’s spending is under budget, and local and federal taxes are lower.

Con Ed business customers and its customers in Westchester County will see a similar rate increase.