The Scottish Police Authority (SPA) said a capital budget underspend of £9.6 million and a revenue overspend of £27.1 million are expected.
The main reason for the overspend is police officer and staff costs, although with “strict workforce planning” these are now being “managed down”.
Of non-pay costs, the overspend is largely a result of not being able to make the level of savings which were targeted, the SPA said.
At the SNP conference last month, Scottish Police Federation (SPF) general secretary Calum Steele said “the scale of the financial challenge facing the police service is enormous”.
Police Scotland are using cars held together with duct tape and cable ties while interview suites for sex assault victims have water coming in and mouldy carpets, he said, blaming decades of under-investment in infrastructure.
An Audit Scotland report published last year warned policing in Scotland could face a funding gap of almost £85 million by 2018/19.
Commenting on the latest overspend forecast, Scottish Conservative justice spokesman Douglas Ross said: “This is a startling increase in overspend and shows that police budgets are starting to spiral out of control.
“It is no secret that Police Scotland are facing budgetary pressures and there are serious questions about whether they have the resources needed to carry out their job.
“The SNP need to explain why this increase in overspend is happening and reassure the public that it will not have a knock-on effect to frontline policing.”
Scottish Labour justice spokeswoman Claire Baker said: “Officers and staff should be getting the support and resources that they need to keep our communities safe, but instead they are facing huge cuts and uncertainty.”
Scottish Liberal Democrat MSP Liam McArthur said: “Last year the national force overspent its day-to-day budget by £18 million. In August we were told it would be £21 million this year. Now they admit it’s risen to £27 million. Police Scotland’s budget crisis is going from bad to worse.
“It’s time that ministers plug the black hole in the police’s budget before hard-working officers and staff pay an even higher price for the SNP’s disastrous reforms.”