There hasn't always been a single cut at the Open Championship, however.
A single British Open cut after 36 holes of play was first used in the 1898 tournament. But in 1968, the R&A switched the British Open to a double cut - one cut after 36 holes, and a second cut after 54 holes. That format remained through the 1985 tournament. For many of those years, the first cut was Top 80 plus ties and the second cut was Top 60 plus ties.
In 1986, the British Open cut rule reverted to one cut after 36 holes, and today it remains Top 70 plus ties.
Other major championship cut rules:
Masters cut rule
U.S. Open cut rule
PGA Championship cut rule
Return to British Open FAQ index

