Mangal dosha forms when Mars sits in the 1st, 2nd, 4th, 7th, 8th or 12th house from the ascendant — and classical texts also check the positions from the moon and Venus. By the widest definition nearly half of all charts are 'manglik', which is exactly why cancellation rules matter more than the label.
The major cancellations: Mars in its own signs (Aries, Scorpio) or exalted in Capricorn; Mars aspected by benefic Jupiter; the dosha present in both partners' charts, which neutralises it for matching; and age-based traditions holding the dosha spent after the late twenties.
What astrologers actually assess is Mars's strength and role in the specific chart: a dignified Mars in the 7th can indicate an energetic, protective partner rather than conflict. The fear-based reading — buy this remedy or face disaster — is precisely what our astrologer code of conduct forbids.
Check your own status with the free Mangal Dosha calculator on Astrojoshya; the result includes the classical exceptions, not just a yes/no.