Difference Between Severity and Priority

While learning the concepts of Software Engineering, we all have come across the two words ‘Severity’ vs ‘Priority’ and always faced the confusion in between them. If we ask any non-technical person the difference between them is nothing. For him, both have the same meaning. But technically as per the Software Engineer the above two are different words having different meanings and used in a different context. Let’s understand them one by one.

Severity

During Test Execution when the tester finds the defect and logs it in any Defect Logging tool like JIRA, Testrail, etc to submit for the developers to work on, it is important for a tester to decide the Priority and Severity based on the defect criticality and complexity so that a developer can deal accordingly. In layman terms, Severity is defined as ‘degree of impact that anything can have’. So Severity in terms of Defect indicates that to what degree a particular defect has its impact on the Software/application. It means to what extent a defect can affect an application. Usually, Severity is defined in terms of financial loss, the company’s reputation and loss of life depending on the application.

Severity is categorized in different categories depending on the impact of the defect on application:

Critical: A defect that hampers the entire application and blocks the user to proceed further or use the application because it is considered as critical. Considering the UI of the application, if the Login Screen of the application hangs and does not allow the user to login and proceed further.
Major: A defect is considered as major if the Major/ important feature of an application is not working as expected or intended to perform. Any significant feature implemented in an application is working completely different from it’s expected behavior then the defect for this will be considered as Major. For example, while doing Online shopping, the user is unable to add products in the cart using Add to Cart feature.
Minor/Moderate: Any feature that is implemented and working differently from the expected behavior but its impacts are tolerable and would not harm the application too much and overall functionality of the application is not affected. A minor defect can wait to be resolved for some time or it can be tackled in the next release of the application. For example in the Terms and Condition page, one of the links is not working.
Low: Any defect that does not harm the functionality but is a valid defect and needs to be corrected. Cosmetic bugs like spelling mistakes and slight misalignment of fonts fall in this category. A few spelling mistakes on a web page are an example of a Low Severity defect.

Priority

Priority in simple English is used in the comparison of two things and where importance is given to one of them. Similarly, in terms of Defect, Priority is the urgency of the defect to be fixed. It refers to the order in which defects need to be fixed keeping in mind it’s severity and business needs.

Developers cannot fix so many defects at the same time so it is important to prioritize the order of the defects which will be fixed by them. Usually, High Severity defects are of High Priority as they demand quick fixing. The priority of defects is categorized as:

High: Any defect that needs immediate attention and needs to be fixed as soon as possible (max 24 hours). Defects that largely impact the end customers and business comes under this category. When the entire application is blocked and testers cannot proceed with further software testing is due to these High priority issues.
Medium: Defects that can wait to get fixed as they are not affecting the major functionality of the application and does not hamper the business and customer falls in this category.
Low: Defects that are filed for changes in the existing design to enhance the customer experience are considered as Low priority defects. These defects need less attention and hence they are considered at last when all the other priority defects have been fixed.

Head to Head Comparison between Severity and Priority (Infographics)

Below are the top 6 differences between Severity vs Priority:

Key Differences between Severity and Priority

Below are the lists of points, describe the key differences between Severity vs Priority:

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The severity of a defect decides the impact on the application whereas Priority decides the order in which defects need to be fixed.
Severity deals with the technical aspects of an application whereas Priority deals with Business Requirements and the impact of the defect on customer requirements.
The severity of any defect does not change as the impact of it remains the same on application whereas Priority changes if the business requirements changes or any defect of more Priority is encountered which needs more attention.

Understanding the Differences between Severity vs Priority through Example

Below are the points, helps to understand the difference between Severity vs Priority:

High Priority and High Severity

In an application, if there is an issue of the login screen and the user is not able to log in then that defect falls in High Priority and High Severity as this needs to be resolved first because the user is blocked and cannot access the application further.

High Priority and Low Severity

If there are some spelling mistakes in the Home page of the application or any other web page which is used frequently is an example of High Priority and Low Severity as Spelling mistakes are not hampering the functionality of application but making a bad impact on a company’s reputation.

Low Priority and High Severity

In Online Shopping website if ‘Add to Cart’ button stops working if the user tries to add more than 500 items in a cart, then the defect is considered as High Severity as the major functionality is not working as expected but Low Priority because it is a very rare case that user add more than 500 items in cart.

Low Priority and Low Severity

If there are some spelling mistakes in a paragraph of a page which is rarely opened by the user is considered as Low Priority and Low Severity because neither it is creating an impact in the functionality of application nor any loss to a company’s reputation as it is rarely opened.

Severity vs Priority Comparison Table

Below is the topmost comparison between Severity vs Priority

Sr.no.	Severity	Priority
1.	Severity is driven by functionality or standards of an application	Priority is driven by business value.
2.	Severity defines the degree of impact that a defect has on application	Priority defines the order in which the defects will be fixed by the developer.
3.	Severity is decided by QA Engineer who is logging the defect	Although tester can decide the Priority, the final decision is taken by the Product Manager keeping in mind the overall view of the product.
4.	Severity value is objective and less likely to change over time.	The priority value is subjective and can be changed over time depending on other defects and project requirements.
5.	Severity is categorized as: Critical Major Minor/Moderate Low	Priority is categorized as: High Medium Low
6.	High Severity defects with Low Priority are considered later after High Priority defects are resolved	High Priority defects are fixed first than High Severity as they hamper the business.

Conclusion

For a Tester, it is very important to know the difference between Severity vs Priority and assign them properly to a defect because even a small mistake in the assignment of Severity can cause a huge loss in an application and company’s reputation. The wrong assignment of Priority can cause a delay in resolving a defect that needs prior attention and hence can hamper the product requirements and financial loss. As a tester while logging a defect, it is important to drill down and understand the impact of that defect on end-user, then assign right Severity and Priority to a defect.