As electricity demand continues to grow, accurate consumption forecasting has become an increasingly important foundation for efficient energy planning, especially at the provincial level where local demand drivers differ significantly from national trends. This study forecasted the monthly electrical energy consumption of the Province of Nueva Vizcaya, Philippines, from January 2016 to December 2025 using Autoregressive Integrated Moving Average (ARIMA) and Seasonal Autoregressive Integrated Moving Average (SARIMA) models developed through the Box–Jenkins methodology. Unlike previous studies that relied on partial datasets, this study used the complete sectoral dataset covering all eight consumer categories, Commercial, Special Purpose Lighting, Public Building, Residential, Non-Lighting, Street Lights, Industrial, and High Voltage, with an average monthly consumption of 113,802 kWh. The analysis revealed a clear upward trend of approximately 11.1% over ten years alongside a stable and recurring seasonal pattern, with consumption consistently peaking between May and September during the dry season. Stationarity was achieved through log transformation, one regular difference (d=1), and one seasonal difference (d=1). Among all candidate models evaluated, ARIMA(3,1,2) recorded the lowest AIC (−701.44) and BIC (−684.76) but failed the residual diagnostic check due to significant autocorrelation in its residuals. SARIMA(0,1,1)(0,1,2)₁₂ passed all diagnostic checks with a Ljung–Box p-value of 0.5367 and achieved superior out-of-sample accuracy with RMSE of 0.01014 and MAPE of 0.0555 and was therefore selected as the best-fitting model. The 12-month forecasts for 2026 project monthly electrical energy consumption between 121,527.40 kWh and 126,178.50 kWh, providing reliable demand projections to support energy supply planning, budget management, and the province's ongoing transition toward renewable energy sources in alignment with SDG 7 and SDG 13.

ARIMA, SARIMA, Box-Jenkins Methodology, Electrical Energy Consumption, Non-Stationary Time Series Forecasting, Nueva Vizcaya, Philippines