What is a Journal Impact Factor?

Definition

The Journal Impact Factor (JIF) is a metric that reflects, on average, how often articles published in a journal were cited during a particular year. Commonly, a journal’s JIF for year Y is calculated as the number of citations in year Y to items published in years Y−1 and Y−2, divided by the total number of “citable items” the journal published in those two years.

How it’s calculated (simplified)

1. Count citations in year Y to articles published in Y−1 and Y−2.
2. Count citable items published by the journal in Y−1 and Y−2.
3. Divide: JIF = (Citations in Y to Y−1 & Y−2 items) ÷ (Citable items in Y−1 & Y−2).

Why it matters

• Used by researchers and institutions to gauge a journal’s reach and average citation performance.
• Influences where authors submit and how libraries prioritize subscriptions.

Limitations

• It is a journal-level average, not a measure of a specific article’s or author’s quality.
• Field differences: citation practices vary widely across disciplines.
• Can be skewed by a few highly cited papers or editorial policies.