Full answer
Instagram requires you to use a web browser — you cannot permanently delete your account from the mobile app. Go to instagram.com/delete/request/permanent, log in if needed, select a reason from the dropdown, re-enter your password, and click "Delete account." The account enters a 30-day deletion queue.
During the 30-day grace period, your profile is invisible to others but not yet deleted. If you log back in during this window, the deletion is cancelled automatically and your account is restored. After 30 days, deletion is permanent and irreversible — your photos, videos, followers, and messages are gone.
Before deleting, download your data. Go to Settings → Your Activity → Download Your Information. Instagram gives you a zip file with all your photos, videos, stories, messages, and comments. Processing can take up to 14 days for large accounts — request the download before initiating deletion.
Consider deactivating instead of deleting if you're unsure. Deactivating (Settings → Account → Deactivate Account) makes your profile invisible and you can reactivate anytime by logging back in. Unlike deletion, deactivation is fully reversible with no time limit.
If you used Instagram to sign in to other apps ("Login with Instagram"), those connections will break when your account is deleted. Go through your connected apps (Settings → Security → Apps and websites) before deleting and update your login method for any apps you still need.