Go to Instagram.com and do the follwoing:
Thanks to Brandon Dies for providing the hint that let me put this back in action.
Due to changes in Instagram's API Terms of Service, I am no longer able to offer the Instagram User ID Finder as a service. I honestly didn't appreciate how popular this service was, until I got eMails from users pointing out that the service was no longer operational.
I apologize for the inconvenience and thank you for your past usage of my tool.
Thank you and take care!
But here is a trick to help you out
window._sharedData.entry_data.ProfilePage.graphql.user.idand hit enter
Steps last updated on 04-June-2016
Further kudos to "Tom", who pointed out the changed code snippet on 01 May 2018