The world’s most elite marathon is just weeks away — and an Ohio man claims he’s already marked at least a dozen runners who cheated their way into the race.

Derek Murphy — a 46-year-old business analyst from the Cincinnati suburbs who spends his free time exposing dishonest athletes — said he’s used a blend of algorithms, online data, anonymous tipsters and official race photos to expose more than a dozen runners who cheated to qualify for the Boston Marathon on April 17.

The 26.2-mile race, known for its strict restrictions on qualifying times, is the world’s oldest annual marathon and the pinnacle of many amateur running careers. Murphy said he reported more than 12 runners to the races in which he accused them of cheating to qualify for the esteemed marathon — and will relay the information to the Boston Athletic Association, which organizes the race, if they are later disqualified.

“Boston typically [leaves] it to the qualifying marathon to police their own races,” Murphy wrote in an email to The Post. “They won’t make a determination on a runner’s race results in another race.”

Murphy said his “best estimate” is that 2 to 3 percent of runners who qualified to run the Boston Marathon in 2015 and 2016 cheated to get to the starting line. That’s as many as 500 runners of the roughly 20,000 who qualify each year, minus charity runners and those granted exemptions, according to Murphy.

Murphy — who focuses on runners who run the marathon significantly slower than their qualifying times — said he identified 57 runners who cheated to run in 2015 and, so far, 30 who cheated last year. But he’s still currently reviewing the results of more than 26,000 people who ran the last race.

Murphy, who admits his best running days are behind him, once completed 10 marathons in the span of 3½ years, so he respects the sport and the dedication required to complete such a grueling athletic feat. He takes it personally when a runner chooses to cut the course.

“I really understand about what it takes to finish a marathon and how people work really hard to get that,” Murphy said. “So yeah, it definitely rubbed me the wrong way that people were taking shortcuts and that’s pushing someone out because their route was oversold.”

Murphy said he was inspired to create MarathonInvestigation.com in 2015 after coming across the story of Mike Rossi, the viral “marathon dad” who gained fame after being scolded for his children’s unexcused absences for taking them to the Boston Marathon. Rossi posted a response to the school’s principal on Facebook, arguing that his kids learned as much in those five days in Boston as they would during an entire school year. But the snarky response led to additional scrutiny of Rossi’s times — and the beginning of Murphy’s latest hobby.

“It turns out that he cut the course in his qualifying run and it kind of blew up,” Murphy said. “I followed that soap opera for a while and I kind of thought to myself: ‘Well, if this guy did this, how many people are doing this and cheating at races?’ So I just pulled up a random result and I found some more right away, so that kind of started my quest for knowledge of how many people really do this.”

There are three main ways a runner would cheat during a marathon, Murphy said, with bib-swappers and course-cutters leading the way. As the name suggests, a bib-swapper gives or sells his or her race number to a faster athlete, while a course-cutter is someone who doesn’t run the full race. There’s also the practice of allowing a faster runner — a so-called “bib mule” — to record a fast time in a qualifying race to secure a spot in the real thing.

The key to rooting out cheaters is analyzing split times, or the duration it takes runners to cover predetermined sections of the course.

“Most races have timing mats,” Murphy explained. “If you run over them and you have a chip in your bib, it registers the time you crossed over the mat so you can look at things like the split between each distance and calculate the pace.”

If someone runs the first half of a marathon in, say, 2½ hours, but then dashes through the second 13.1 miles in 90 minutes, it’s usually a red flag to dig deeper, Murphy said.

“It kind of adds up,” he said.

Murphy’s most recent takedown was last week when he chronicled his investigation into Jane Seo, a New York City food blogger and Huffington Post contributor whose second-place finish in the Fort Lauderdale Half Marathon was disqualified after she admitted cutting the course. Initially, Seo denied cheating and accepted the second-place prize, but Murphy said he got an anonymous tip urging him to investigate further.

“Digging in, it was pretty obvious,” he told The Post. “Just by looking at it, she had a large negative split, where her pace at the end of the race was much faster than when she started and it was 85 degrees in Florida that day. Nobody would run that kind of a split, so that was pretty obvious.”

Seo’s results equated to a pace of 7 minutes and 9 seconds per mile in the first 10 kilometers and a near-impossible backend pace of 5 minutes and 25 seconds in the remaining 11.08 kilometers.

Seo, who did not return a message seeking comment, later posted her stats on Strava — a mobile app and website for athletes to post their routes, times and other data — but Murphy noticed that the data was more in line with a person riding a bike than stomping the course with their two feet.

“I was more fascinated with this one for a couple reasons,” Murphy said. “One, she took second in the overall half-marathon and secondly, steps that she took in order to cover that up. She was really trying to cover her tracks.”

But Seo’s Garmin GPS watch would ultimately be the “nail in the coffin,” said Murphy, who bought race photos to confirm that she didn’t run the entire distance. Murphy got his hands on a finish-line shot and noticed Seo’s Garmin was, in fact, turned on at the time. But the display did not lie: 11.65 total miles, or 1.45 miles short of a full half-marathon.

Even with his sophisticated tactics, Boston Marathon officials say Murphy’s estimate of potential cheaters “seems high.”

“We rely on marathons to submit accurate results to us for verification purposes, and ultimately entry into the Boston Marathon,” T.K. Skenderian, communications director for the Boston Athletic Association, wrote The Post in an email. “If some incident is verified by the directors of a race and they adjust their results, we then make adjustments as appropriate.”

Tom Grilk, BAA’s executive director, told the Boston Globe last April that 23 finishers from the 2015 Boston Marathon were expunged after checkpoint data could not verify that they completed the entire course. A total of 50 finishers were disqualified for the same reason in 2014, when more runners participated since it marked the first race following the Boston bombings.

But Murphy, an admitted “numbers geek,” thinks his efforts will cut into those numbers and perhaps shame some would-be cheaters into running the right way.

“Really, this kind of started as a hobby, but then once it started getting some attention, it began to resonate with people,” Murphy told The Post. “It’s kind of what I do at night instead of sitting and zoning out in front of the TV or a computer screen. It’s like a puzzle.”