generating popup after duration of time

Question

Hi,

    i have created the loin page with storing in  database user id and password,also generated the change password page .i want to generate 

popup before  expiring  the password .there should be message like in 2 days your password is expired please change your password. how can i do that i do not have any date time in database that when i have changed last time my password.

Please give the solution with code.

Thanks,

Vibhakar singh