A full stop is used:
- to indicate the end of a sentence. Put 1 space after a full stop, not 2. The old typewriting convention of putting 2 spaces after a full stop has been dropped. Two spaces can actually detract from, rather than improve, readability and can cause problems with formatting
- to separate elements of the username (before the @) and domain name (after the @) of an email address
- to separate elements of the domain name of a URL
- to separate hours from minutes in times of day (a colon can be used as an alternative)
- to separate a filename extension from a filename in a computer file
readme.txt document.docx
- to indicate ring size in chemical names.
Full stops are not recommended:
- at the end of headings
- after a person’s initials (see References).
Also use minimal full stops in abbreviations and contractions (see Acronyms and initialisms).
But follow the style of your organisation or journal, as appropriate.