The Impact Factor from Journal Citation Reports is the oldest citation metric, first calculated in 1975. It is a ratio of the number of current year citations to the citable items published in that journal during the previous two years: 

Impact factors do not account for disciplinary differences in citation rates or how fast citations accumulate, so it's important to compare a journal to other journals in the discipline by looking at rank, quartile, and percentile. 

For the 5-year Impact Factor, citations to articles published in the previous 5 years are included in the denominator instead of the previous 2 years. This metric allows disciplines with slower citation turnaround times to show their impact over time. This is the calculation for the 2015 5-year Impact Factor:

Impact Factors are problematic for a couple of reasons beyond those listed for general impact metrics. 

• They are calculated for a limited set of journals. Impact Factors are calculated for journals included in Web of Science's Science Citation Index and Social Science Citation Index, which are selective instead of comprehensive. Not all journals will have an Impact Factor. 
• They are proprietary, and access is subscription-based. Not everyone has access to Journal Citation Reports. 

1. Open Journal Citation Reports.

2. Enter your journal title. As you type a suggested title may be displayed: select it and complete the search.

3. Yearly impact factor and recent trends are available just under the journal profile. 

4. Scroll down to the middle of the page to find the "Rank by Journal Impact Factor" box which allows comparisons to other journals in the same subject category.

1. Open Journal Citation Reports.

2. Enter your journal title. As you type a suggested title may be displayed; select it and complete the search.

3. Change the small drop down at the top left from current year to "All years". 

4. Scroll down under the profile to view the metrics table and look for the 5-year Impact Factor column.