The messages appear as invitations to events but are sent by spammers not the brands they feature.
The "report junk" button has been added to Apple's iCloud.com site and is expected to be included in an iOS update soon.
The calendar bug was heavily exploited this year around Black Friday.
Clearing out the bogus messages was frustrating because deleting the invitation sent an acknowledgement to the spammer it came from, revealing that an account was live.
Some people reported that declining an invitation led to them receiving more spam from the same source.
The spam invitations appear to come mainly from Chinese email addresses.
The reporting button removes the junk invitations from a person's calendar and lets Apple know about the message.
The button automatically appears on invitations sent by people not in someone's contacts list.
Until iOS is updated, anyone wishing to tackle the spam on their calendar must visit iCloud.com and click to report the faked messages.
The invitation will then disappear from all synched calendars.
Late last month, Apple apologised for the sudden influx of calendar spam and said it was working on ways to fix it.
Before the introduction of the reporting system, many people fixed the problem by creating a second calendar only for spam.
They moved all the junk invitations into that calendar and then deleted it.
Apple is tackling an outbreak of spam on iPhone calendars by introducing a button that lets users report the junk appointments.