People are often uncertain about whether or not to use full stops/periods in abbreviations. Here are some guidelines:
1. In both American and British English, if you are using initial letters to represent words, you don’t normally need to put a full stop/period after:
2. In American English, however, it is common to use a full stop/period as an alternative style for certain abbreviations, in particular:
USA or U.S.A.
US or U.S.
3. If an abbreviation consists of the first and last letters of a word, the American rule is to include a full/stop period at the end:
4. The British norm, however, is not to use a period at the end:
5. If the abbreviation consists only of the first part of a word, then you should put a period at the end:
Wed. (= Wednesday)
Dec. (= December)