Inflation Dynamics in the Philippines: Trends, Volatility, Seasonality, Commodity-Group Relationships, and Forecasting Using Monthly CPI Data, 2019–2026

This study examined inflation dynamics in the Philippines using monthly Consumer Price Index (CPI) data from January 2019 to August 2026. It assessed inflation trends, average and dispersion, volatility, seasonality, relationships between overall inflation and commodity groups, period-specific changes, and forecasting performance. Using descriptive statistics, seasonal testing, Pearson and Spearman correlations, multiple regression, interaction analysis, and out-of-sample time-series forecasting, the study analyzed 92 monthly observations from the Philippine Statistics Authority. Overall inflation accelerated from 2021, reached elevated levels during 2022–2023, moderated through 2025, and increased again during January–August 2026. Food, housing, transport, and restaurants and accommodation services showed strong positive relationships with overall inflation. Monthly inflation did not differ significantly across calendar months (H(11) = 2.257, p = .997). The regression model explained 99.9% of variation in overall inflation, although severe multicollinearity limited interpretation of individual coefficients. Relationships with selected commodity groups also strengthened during the most recent inflationary period. Among evaluated forecasting models, SARIMA(1,1,1)(1,0,1)[12] produced the lowest validation errors, with MAE = 0.493, RMSE = 0.751, and sMAPE = 16.338. The findings indicate that Philippine inflation is dynamic, component-linked, and period-sensitive, supporting disaggregated monitoring and cautious, model-based forecasting with uncertainty increasing over longer horizons.