Nigeria's National Bureau of Statistics (NBS) will change the way it calculates inflation as last year's rebasing measure could make December's year-on-year inflation appear artificially high, the agency said on Tuesday.

The rebasing, the first in 15 years, set December 2024 as the index reference point, a move officials said would distort December data without reflecting actual price trends.

December inflation data is due to be published on Thursday. Analysts are predicting a sharp rise in the headline figure to 30% from 14.45% year-on-year in November.

"The widely reported 30% figure for December is only a projection and not from the bureau,” said Ayo Anthony, head of prices at NBS.

Consumer inflation peaked at nearly 35% in December 2024, then fell sharply after the statistics office revised its base year and food prices eased.

"This spike is not the real inflation rate; it is an artificial spike caused by the base effect from rebasing," Anthony said.

"We are removing the single-month index reference period and replacing it with a 12-month reference period for 2024 to report actual inflation."

Anthony noted that while countries like South Africa and Kenya use a one-month base, Nigeria's sharp price increases make that method unsuitable.

Prior to last year's rebasing, Nigeria rebased its inflation data in 2009.

"We haven't rebased in 15 years, so some of the base effect playing out is due to that lag," said Bonaventure Nwosu, head of communications at NBS.

"Whatever spike you see for December is a one-off and should not be interpreted as real inflation. From January 2026, figures will normalise and reflect actual market conditions."

The bureau said the new methodology will provide a clearer picture of inflationary pressures in Africa's most populous nation.