OTTAWA (Reuters) - Canada recorded its first monthly budget deficit of the fiscal year in August, a hefty C$2.34 billion ($1.79 billion), due primarily to updated actuarial estimates of pensions and other future employee costs.

The Finance Department said in its monthly Fiscal Monitor on Friday that the adjustments in the actuarial estimates of costs of pensions and other future benefits were driven largely by changes in the interest rates used for the calculations.

In August 2014, the government had adjusted those costs down and then this August it recorded an upward adjustment.

This was the main reason why direct program expenses - excluding transfer payments - jumped by 68.7 percent from the previous year.

Every other month in the fiscal year, which starts in April, had shown surpluses, and the fiscal year to date still has a C$2.82 billion surplus, compared with a C$1.12 billion deficit for the same period last year.

Canada posted an overall budget surplus for the 2014-15 fiscal year of C$1.9 billion, the first time the books had been in the black since 2007-08.

($1=$1.31 Canadian)