A cover letter actually changes your chances when a posting explicitly asks for one, when the application otherwise gives you no room to explain something the CV alone cannot, such as a career change or a gap, or when the role and company genuinely warrant showing you have done more than send the same document everywhere; it is mostly extra effort with little payoff when none of those apply and the posting accepts a CV on its own, since a generic letter added out of habit rarely tells a reader anything the CV had not already covered.
The clearest case: the posting asks for one
If a job posting explicitly asks for a cover letter, that request settles the question on its own, independent of how much the letter is likely to be read closely. Skipping a requested cover letter reads, at minimum, as not having followed the application's own instructions, and a reader who notices that before reaching the actual content of the application starts from a worse position than one who simply saw a complete submission. This holds even for a posting where the cover letter otherwise seems like a formality that few applicants bother to read carefully; the instruction itself is the signal, not a judgement about how closely anyone will read what gets written in response to it.
When a cover letter fills a gap the CV cannot
A CV is built to present facts, dates, roles, education, skills, in a structured, easily scanned format, and that structure is exactly what makes it a poor place to explain something that needs context rather than a line item. A career change, a gap in employment, a return after time away, or a genuinely unusual path into the target role are all situations where a short paragraph of explanation does more work than trying to fit the same explanation into a CV bullet where it does not naturally belong. In these situations, a cover letter is not optional politeness, it is the one part of the application built to carry that kind of explanation, and skipping it leaves the reader to guess at a question the letter could have answered directly.
When a cover letter is unlikely to move the needle
At the other end, a cover letter is more often extra effort than a meaningful factor when the posting does not ask for one, the CV alone tells a complete and unremarkable story, no career change or gap needs explaining, and the application process itself suggests high volume, a simple online form with no free-text field for a letter, for instance. In this situation a generic cover letter, restating the CV's own content in paragraph form without adding anything new, is unlikely to change how the application is read, and the time spent writing one might do more for the application if spent instead making sure the CV itself is tailored to the specific posting. This is not the same as saying a cover letter can never help in this situation, only that its expected value is lower, and it is reasonable to treat it as optional rather than mandatory when none of the stronger signals above are present.
A quick rule of thumb
Write a cover letter when any of these hold: the posting asks for one explicitly, the application process gives space for one and the role is genuinely competitive or a strong fit worth explaining, or there is something about the candidate's path, a change of field, a gap, an unusual route into the role, that the CV alone cannot explain clearly. Treat it as optional, and reasonably safe to skip, when none of those apply and the CV on its own already tells a complete, easy-to-follow story for the role being applied to.
Illustrative example: two scenarios, and how the answer differs
Scenario one: a posting for a role the candidate has direct, recent experience in explicitly invites an optional cover letter through a simple online form, and the candidate's CV already tells a straightforward story with no gaps or unusual turns to explain. Skipping the letter here is a reasonable choice, since nothing about the situation needs explaining and the letter would likely restate what the CV already shows.
Scenario two: a posting for a role in a new field for the candidate, who is changing direction after several years in a different kind of work, explicitly requests a cover letter alongside the CV. Here, the letter is doing real work: it is the one place in the application built to explain why the change makes sense and what carries over from the previous field, something a CV's bullet-point format is not built to state clearly on its own.
Writing one, once it is worth writing
Once the decision is to write a cover letter, the cover letter guide covers how to structure one and how to open without wasting the first line. CVBuilderKit can draft a matching cover letter directly from a CV already built in the Orbit template, pulling from the same underlying content rather than starting from a blank page, up to a set number of letters per CV; start building the CV itself first if that has not been done yet, since the letter draws from it once it exists.