juniorTime Series
What is seasonality in time series data?
Updated May 15, 2026
Short answer
Seasonality is repeating patterns in time series at fixed intervals.
Deep explanation
Seasonality refers to predictable and recurring fluctuations in data over fixed periods such as daily, weekly, or yearly cycles. It is a key component of time series decomposition along with trend and residual. Identifying seasonality helps improve forecasting accuracy.
Real-world example
Retail sales increase every December due to holidays.
Common mistakes
- Confusing trend with seasonality.
Follow-up questions
- What is seasonal decomposition?
- What is additive vs multiplicative seasonality?