Tense is generally defined in ways such as: the relationship of the form of the verb and the time of the action it describes.
 How many tenses in English?
If we confine ourselves to the form, then English has only two simple (i.e. unmarked for any other aspect) tenses, as shown in the pairs play/played, work/worked, want/wanted, sing/sang. The first of these forms is traditionally called the Present Simple, the second the Past Simple.
However both tenses in English can refer to past, present, future and general time; the traditional names are therefore misleading, and some writers prefer to call the ‘present’ tense the Unmarked (Tense), and the ‘past’ tense the Marked (Tense).
 The future
Forms with WILL, sometimes referred to as the "future tense", are simply examples of one use of a modal verb that can refer to the future, but often does not. There are at least four other commonly used ways of referring to the future in English, and none can be singled out as a ‘future’ tense.
Some writers use the word tense for such forms as I am/was working and I have/had worked, but these are better considered as aspects.
- Richards , Jack C, Platt, John and Platt, Heidi (1992) Longman Dictionary of Language Teaching & Applied Linguistics (2nd Edition), Harlow: Longman