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may i say both

"let me know when it is available"

and

"let me know when it will be available"

?
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Hi,

Let's assume that you speak at 1pm and 'it' becomes available at 3pm.

"let me know when it is available" I'd expect you to say to me, at 3pm, 'It's available now'.

"let me know when it will be available" I'd expect you to say to me, at 1pm, 'It will be available at 3pm'.

However, we do not always speak with care. We sometimes interchange these expressions.

Best wishes, Clive
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Yes. You may say either one.
"when" is not used with "will" when it specifies the time at which something happens or should happen.
"when" can be used with "will" (or without "will") in indirect questions.

Therefore, in the reading of "at the time it happens",

Let me know when it is available.

asks the person to inform you at the time that it becomes available, not before.
"when it will be available" is not possible for this reading!

In the indirect question reading, you are asking for some information to be given as an immediate response, namely the time of availability.

Let me know when it is available.

is then "When is it available? Tell me."
The present tense here may be being used in habitual aspect, the answer then being of a form like "It is available on Mondays and Wednesdays." Or it may be being used in a perfective aspect - i.e., as a future, meaning "When will it become available?", and the form of the answer will then be something like "next Friday".

Again in the indirect question reading, requesting information immediately:

Let me know when it will be available.

only the future (perfective aspect) interpretation seems possible, not the habitual, at least to my ear.

Personally, I do not typically use the one with "will".

CJ
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Comments  
We can also say " PLease let me know when it becomes available"
Students: Are you brave enough to let our tutors analyse your pronunciation?
erm, interesting that if we google the said sentence out well get the following ratio: 2 050 / 428 matches (with will&w/o)