The Liberal government ran a $7.8-billion deficit over the first half of the fiscal year, largely due to a 7-per-cent hike in program spending.
The figures are contained in the latest Fiscal Monitor tracking report released monthly by Finance Canada.
The report shows Ottawa ran a $2.4-billion deficit in September, compared with a $1.2-billion deficit in September, 2015.
The cumulative deficit over the first six months of the fiscal year stood at $7.8-billion, compared to a surplus of $1.6-billion over the same six-month period a year earlier.
The report does not project whether the spending and revenue trends are in line with the most recent forecasts from Finance Minister Bill Morneau.
Monthly figures for the bottom line can fluctuate significantly.
Mr. Morneau's Nov. 1 fiscal update projected a $25.1-billion deficit for the current 2016-17 fiscal year. The deficit has been forecast to reach $27.8-billion the next year before shrinking gradually to $14.6-billion by 2021-22. Mr. Morneau has not provided a timeline for when the federal government will return to a balanced budget.
The government's fiscal plan is at odds with what the Liberals promised during last year's election campaign.
The party's 2015 campaign platform promised "modest short-term deficits of less than $10-billion in each of the next two fiscal years" and that after that "the deficit will decline and our investment plan will return Canada to a balanced budget in 2019."
The federal government posted a $1.9-billion surplus in 2014-15 after six straight years of deficits.
The final bottom line for 2015-16 was a small deficit of $987-million.
A closer look at Friday's Finance Canada report provides a more detailed look at spending trends.
Over the first six months of the year, program spending is up 7 per cent or $8.9-billion.
This is due to a 5.3-per-cent increase in elderly benefits due to demographics, a 7-per-cent increase in Employment Insurance benefits, and a 15.4-per-cent increase in children's benefits due to the new Canada Child Benefit.
Persistently low interest rates continue to help Ottawa's finances.
The government saved $1.4-billion, or 9.8 per cent, on public debt charges over the first six months of the fiscal year because of lower interest rates.