What's the difference between an 'unfollower' and someone who 'doesn't follow back'?

The computed result is the same. Both mean 'an account that you follow but that doesn't follow you back.' The nuance differs, though: 'unfollower' often implies someone who used to follow you and then stopped, while 'doesn't follow back' is used for someone who was never a mutual in the first place.

Can I find out when someone unfollowed me?

Instagram doesn't provide the exact time of an unfollow, so you can't know it. The list does, however, include information about when you followed that account, which can help you clean up old one-way follows.

Find People Who Don't Follow You Back on Instagram

Have you ever felt that your following count is high, but few people actually follow you back? By pulling a list of accounts that you follow but that don't follow you back, commonly called "non-followers", you can see it all at a glance. This article shows you how to find that list for free, with no login and no app.

How Are "Non-Followers" Calculated?

The principle is simple set subtraction. When you subtract your followers list from your following list, what remains are the accounts that "I follow but that don't follow me back." Conversely, accounts that appear on both lists are mutuals. Mewbula runs this calculation automatically inside your browser and shows you the result as a list.

How to Find Them (3 Steps)

Download your information — Export your followers and following data as JSON. (See how)
Upload the file — Upload the ZIP directly to the Instagram unfollower checker.
Check the list — The "unfollowers" tab is exactly your non-followers list. You can jump straight to each account's profile or save the list as text.

How Do You Use the List?

Clean up — Unfollow old one-way follows to keep your following list light.
Manage mutuals — Use mutual status as a basis to focus on your most active relationships.
Track — Download the file periodically and compare to see how your relationships change over time.

A Note on Accuracy

Because Instagram's "Download your information" file is stored, past data rather than real time, it can differ slightly from your actual status. Even if the list isn't perfectly accurate, keep in mind that this is a structural limitation of the data, not a mistake in your settings. For the broader context, see How to check Instagram unfollowers.