Have colleagues resorted to nicknaming you “the late John Smith,” even though you’re very much alive? Do the clocks at work always seem to be running 15 minutes fast, except when it’s time for you to go home? If you were the star of “High Noon,” would the producers change the title to “12:30ish”?

Being late all the time can cost your company money — and you your reputation. It’s a habit that isn’t as easy to break as people might think, says Diana DeLonzor, a San Francisco time management consultant and author of “Never Be Late Again: 7 Cures for the Punctually Challenged.”

“Telling a late person to be on time,” she said, “is like telling a dieter, ‘Don’t eat so much.’ ”

The differences between late people and their on-time counterparts are usually far greater than just minutes. In her book, DeLonzor describes a 1997 study of 225 people that she did with San Francisco State University, giving them personality tests to try to determine what causes chronic lateness.

“As it turned out,” she writes, “the late scored higher in several areas, including anxiety and distractibility, while placing somewhat below the timely in the areas of self-esteem and self-discipline.”

DeLonzor, who used to be chronically late herself, said in an interview that late people are most often procrastinators. They have trouble resisting the immediate gratification that comes from not having to perform a task right away, and sometimes actually enjoy the adrenaline rush of putting something off until the last minute. And those habits have become ingrained, often from the time they were students.

“Really smart kids tend to be the biggest procrastinators because they were able to get away with it more,” she said. “Their habits were created long ago.”

Most late people underestimate how long it takes to accomplish everyday tasks. They also aim to arrive at places exactly on time, rather than a few minutes early, then blame their tardiness on common occurrences like traffic instead of changing their habits.

“They need to ban that phrase, ‘OK, if I just hurry, I can squeeze in one last thing,’ ” DeLonzor said.

The book lists seven potential cures, depending on the cause, but DeLonzor explained that most people do best by simply relearning how long tasks take. They might have managed to commute to work one time in 15 minutes, so that amount of time sticks out in their mind — even if now the commute regularly takes half an hour.

She suggests you spend a week keeping track of how long your regular activities take — such as getting ready for work — and then use the slowest of those times as your baseline for the future.

Another tactic she recommends is that each night, you list three tasks you will do the next day that will be done early, such as showing up for an appointment early or mailing in a bill before its due date.

Some chronically late people do feel bad about the consequences, but others are more oblivious, DeLonzor said. If your loved one or colleague is among the tardy, she said, don’t take it personally, but certainly speak up if it’s causing problems for you.

She suggests talking with the late person, explaining how the problem is causing you to lose respect for him. If you he understands the problem and wants to change, sometimes a set of penalties works, such as having him pay for dinner or dessert if he’s more than 15 minutes late.

If the repeat offender is your boss or you simply can’t stomach a confrontation, DeLonzor’s Web site (www. neverbelateagain.com) lets you e-mail an anonymous citation from the “National Department of Punctuality and Attendance,” urging the punctuality challenged to get their act together.

DeLonzor said another cause of lateness is when procrastinating workers fool themselves into thinking that the delays actually help the quality of their work. They will often say something like “I work best in a crisis.”

“It’s a last-minute job, and it really shows it,” she said. “What they really mean is, ‘I only work in a crisis.’ ”