She’s going the extra mile for this birthday.

A Manhattan high school senior will become one of the youngest people to ever run in the New York City Marathon Sunday — but the historic triumph is just a bookend for an already-riveting week for the teenager.

Lucy Weld is turning 18 on Nov. 1, the day of the 50th annual race, a coincidence she considers kismet, considering she’s always dreamed of accomplishing the five-borough feat.

“Running it on my birthday, I feel like I have to do it!” the Upper East Side teen told The Post ahead of race day.

“I’m really excited! I’m a little bit nervous, but I feel like it’s really cool to have that under my belt.”

Weld had long dreamed of running the marathon. And since the rules dictate that participants must be at least 18, 2026’s running of the 26.2-mile race couldn’t come at a better time for her.

The Nightingale-Bamford School senior had grown up watching the heavy stream of racers near the finish line — and even suffered through the road blockages that made getting to her childhood soccer games a headache.

What she didn’t anticipate was squeezing her first-ever marathon into one of the most exciting weeks of her young life so far.

Weld, as captain of her soccer team, led her teammates to their first league championship win in 13 years on Wednesday — cinching the win just days before the marathon.

“I really do enjoy running and — this sounds really cliché — but I enjoy challenging myself and I feel like this is the ultimate way to do that physically,” the soccer winger said.

Weld is running this year’s race on behalf of the $71,000-a-year Nightingale-Bamford School, which is raising money to benefit The Pine Ridge School in South Dakota, its partner institution and the only all-girls school on a Native American reservation.

Typically, the Nightingale Team is comprised solely of alumni and faculty — making Weld the first current student to ever run the marathon in its ranks.

And since her birthday falls on race day, Weld is also the youngest of the more than 60,000 runners competing in this year’s marathon.

Road Runners rules require racers to be at least 18 years old, an age limit that was set in place in 1988, making it fair to say Weld can also count herself among the youngest to compete in the entire history of the race.

Wesley Paul will forever remain the record holder, however, after running the first-ever New York City Marathon in 1977 at the age of 8.

Weld is most looking forward to the final few miles along Fifth Avenue — and not just because it means the finish line is within reach.

“This is where I normally run, so it’ll be familiar to me. But I’ve also just heard that the crowds and energy there are incredible and so I’m really looking forward to that!” she said.

Weld expects to celebrate her 18th birthday and first-ever marathon with a quiet family dinner at home.

The real party will come the following week when she’s had a chance to recuperate.