What is the right time to apply for H4 extension?

[Umesh]

My employer recently started my H1b extension but i haven't received the receipt number yet.

I want to know when should i apply for dependent's H4 extension. Should i just go ahead and file for H4 extension or should i wait for my H1b receipt number?

Thanks

[gopalakrishnach]

Since yours is H1B extension you will surely get receipt number. 

[Umesh]

Thanks @gopalakrishnach. So should i apply for dependents H4 extension as well even though i dont have my H1b receipt number?

[gopalakrishnach]

If dependents visa/approvals are still valid, I advice you to wait till your H1B is resolved... If they are not valid you need to apply H4 visas there is no other way...