The National Bureau of Statistics has said that it would ‘normalise’ Nigeria’s inflation data for December 2025 over a projected spike in last month’s Consumer Price Index.

This was disclosed on Monday during a virtual stakeholders engagement convened by the NBS and the Nigerian Economic Summit Group

NBS explained that the expected spike in inflation is driven by technical base effects linked to the recent rebasing of the inflation series rather than changes in economic fundamentals.

The PUNCH reported that multiple analysts have projected a spike in the headline inflation for December on the back of base effects. Projections ranged from 31.4–32.4 per cent year-on-year.

Providing the official position of the Bureau, Statistician General of the Federation and Chief Executive Officer of NBS, Adeyemi Adeniran, explained that the projected December spike stems from the rebasing of the CPI, which adopted 2024 as the new base year after a 15-year gap from the previous 2009 base.

He emphasised that base effects are a common feature of statistical practice, particularly in index-based measurements.

“Following the rebasing exercise and the methodology adopted for December 2025, a significant artificial spike in the inflation rate is expected, as some analysts have already projected. This spike arises from the base effect, with December 2024 equated to 100 following the rebasing.

“Base effects are common in statistical practice, particularly when comparing data across periods with unusually high or low prices. They are neither unexpected nor unusual.

“However, when such effects occur, especially when they are artificial and arithmetic rather than reflective of structural changes in the economy, it is essential to clearly communicate and explain them to users,” he stated.

Adeniran said transparency and accountability guided the Bureau’s decision to address the issue proactively.

“Transparency requires that we provide a clear picture of actual price changes rather than simply reporting an artificial spike that does not reflect economic realities. This is why we convened this meeting to inform our critical stakeholders and users of our data,” he added.

In his opening comments at the session, the NESG Chief Executive Officer, Dr Tayo Aduloju, underscored the growing importance of credible inflation data as Nigeria transitions from economic stabilisation to consolidation.

“As the economy shifts from stabilisation reforms to consolidation reforms, the role of official statistics—especially the CPI—becomes not less important, but very, very crucial,” Aduloju said.

He noted that preliminary assessments suggest inflation figures could record temporary technical spikes, stressing that such outcomes should be carefully interpreted.

“During periods of acute instability, headline inflation serves as an alarm bell.

“But as we move from managing crisis to managing growth, CPI statistics must help us understand inflation dynamics properly, not just react mechanically to headlines,” he said.

Aduloju warned that misleading inflation signals during the consolidation phase could undermine hard-won gains.

“In this phase of macroeconomic transition, policy errors can be very costly,” he said. “Credible CPI statistics anchor policy coherence, guide monetary policy calibration, inform fiscal planning, shape wage negotiations, and influence investment decisions.”

Delivering the technical presentation, Director of Price Statistics at NBS, Dr Ayo Anthony, detailed the methodological challenges created by the rebasing exercise and the steps taken to resolve them.

“The last CPI rebasing was done in 2009, and ideally this exercise should be carried out every five years,” Anthony said. “Because of this 15-year gap, consumption patterns changed significantly, leading to the introduction of over 400 new products into the CPI basket and the removal of more than 200 items.”

He explained that linking the new CPI series—with 934 products and a 13-division COICOP classification, to the old series created unavoidable statistical complications.

“To compute year-on-year inflation, we had to link the rebased CPI to the old series,” he said. “Using December 2024 equal to 100 allowed that linkage, but it also introduced the base effect we are now seeing.”

Anthony warned that without adjustment, the December 2025 inflation figure could appear significantly inflated.

“For transparency and accountability, we are engaging stakeholders to explain the statistical solution, which aligns with global best practice. Projections show that without adjustment, December year-on-year inflation could appear excessively high due solely to arithmetic base effects, rather than underlying economic conditions.

“To address this, NBS will apply a normalisation process, as provided for in the CPI Manual 2020 (Chapter 9, Section 9.125), referred to as maximisation of the index reference period. Where a single-month reference period proves unsuitable, the manual recommends using a three-month or 12-month average. Accordingly, instead of December 2024 equalling 100, the average CPI from January to December 2024 will equal 100.

“This adjustment removes the artificial base effect and presents a more accurate picture of inflation dynamics. While this adjustment affects published figures for January to December 2025, the impact is not significant and will be clearly communicated to stakeholders,” he explained.

He added that while the adjustment affects inflation figures from January to December 2025, the impact on previously published data is minimal and will be clearly disclosed.

“We are not hiding anything. For transparency, we will still make reference to the artificial spike in our reports,” Anthony said.

The NBS official also emphasised that the decision was not made in isolation, stating that technical partners, including the International Monetary Fund, the World Bank, and the Central Bank of Nigeria, were consulted to arrive at this decision.

Looking ahead, he noted that the base effect would no longer apply from January 2026, as inflation calculations would rely solely on the rebased CPI basket.

“From January 2026 onward, the base effect will no longer apply, as comparisons will be made using actual index values from the rebased basket,” he said.

The NBS used the engagement to reiterate the importance of regular rebasing of macroeconomic indicators.

Anthony said, “The key lesson here is the need to rebase CPI and GDP as at when due. When rebasing is done every five years, we avoid these unusual distortions.”

The NBS reaffirmed its commitment to sustained stakeholder engagement, methodological rigour, and clear communication as it seeks to strengthen confidence in Nigeria’s official statistics.