This is due mainly to the rebasing of its economy in February, the treasury said on Friday.
"After rebasing the GDP it has now reduced to 5.2 per cent.
It would have been 6.2 per cent in the old GDP," the Secretary to the Treasury Fredson Yamba said, adding that spending cuts had also influenced the deficit forecast shift.
“These measures are not one-off but will continue over the medium to long-term, leading to fiscal consolidation and fiscal prudence," Yamba added.
(WATCH VIDEO: Zambia GDP adds 25.2%)
Yamba said the treasury would maintain its year-end inflation target of 6.5 per cent, despite the kwacha currency plunging to its weakest level on record against the US dollar this year, which had threatened to push up prices.
Zambia's economy was projected to grow around 6.5 per cent this year, driven by agriculture, mining, manufacturing, construction and energy sectors, he said.
Between 2015 and 2017, economic growth will average around 8 per cent, he said.
The IMF said on Friday that Zambia's economy continued to grow at a rapid pace but fiscal and exchange rate fluctuations were a risk to economic development.