Millennial parents dream of a golden age gap between kids. It comes with a catch.

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After Kristin Darnell had her first child at 34, when her husband was 40, the plan was to try for their second in two years. But when the time came, they weren't ready.

One of the biggest concerns was the cost of childcare. Having two kids in day care at once would have been astronomically expensive, even though Darnell works in ingredient sales for the food and beverage industry, and her husband is an engineer.

The couple was eventually able to welcome their second child a little later, thanks to IUI, ending up with a three-and-a-half-year age gap between their children, who are now 6 and 3. Last year, with both kids in day care, they spent about $37,000 for the year — a little over $3,000 a month. Darnell estimated that they saved about $200 to $300 a month in childcare costs due to the wider age gap.

"Family planning's a tricky thing; you have one idea before you start and then sometimes that idea shifts," Darnell, now 40, told Business Insider.

This is the spacing dilemma, and Darnell's family isn't the only one facing it. More than a quarter of moms in their 20s expect to have their next child in two to five years, a 2026 CDC report shows. But that figure drops below 10% for moms in their 30s.

Waiting longer between kids can help spread out day care costs and mean only having one child in diapers at a time. But as millennials are having kids later, their hopes for a "golden" age gap can collide with another clock: declining fertility. If parents want more breathing room between babies, waiting can come with trade-offs and benefits.

The delicate art of cutting childcare costs

Today, many millennials tap out at having two kids. Part of that is due to financial constraints.

While many expectant parents are aware of the notoriously exorbitant childcare costs, Karen Guzzo, a sociology professor at the University of North Carolina, said they can feel even more discouraged after they've had their first baby. "It's not until you actually get into the nitty-gritty yourself that you're like, 'Wow, this is really expensive,'" Guzzo, who's also the director of the Carolina Population Center, said.

For most Americans, childcare for one kid is steep. The average cost of day care ranges from roughly $7,600 to $24,000 a year, depending on the state and child's age. Things get more financially precarious with two: In nearly all US states, the average annual cost of childcare for two kids at once exceeds mortgage or rent payments. For some parents, it means paying up to $50,000 annually for day care alone.

Factor in other expenses, from car payments to student loans, and many parents start tweaking their timelines. Having a 3- to 4-year age gap between kids means having only one kid in day care or with a nanny at a time; the oldest might already be in preschool, which is offered as a free, public option in most states.

Angela Donahue, who works in product marketing in Renton, Washington, knows what it feels like on both sides of the gap. She put a 4-year age gap between her first and second child (who are now 9 and 5), and a 2-year age gap between her second and third (who is almost 3). While she preferred the wider age gap, she had her third child sooner, at 40, due to age concerns.

With her first and second kids, she said they overlapped in day care for about 6 to 9 months. But she's felt more of a financial strain with her two youngest in day care together over the last two years. Right now, it costs her and her husband roughly $5,000 a month — more than their mortgage.

"I heard some joke about when you have children, people are always like, 'You've got to save for college' — it's like, 'No, college is far away; you've got to save for day care,'" Donahue, 43, told Business Insider.

She said she's excited for the fall, when her second child will be off to kindergarten: "It's definitely really expensive, and we always celebrate when the next one is off to school."

Balancing less visible tolls

To feel comfortable having more kids, many working millennial parents want more career stability. Timing, particularly for mothers, can play a huge role.

"Had I had back-to-back babies, I think it would've taken a larger toll on my ability to advance my career," Darnell said.

Donahue also felt that spacing out her first and second children more was helpful for her career trajectory. For starters, it took her time to adjust to being a new mom. At the same time, she wanted to "keep the momentum going before taking another break," she added, something that felt easier to do when she waited longer to have her second child.

While some research finds that being a parent can improve one's reputation at work, other studies find that a "motherhood penalty" still exists. One 2026 systematic review of 79-peer reviewed journals found that mothers generally faced barriers to career advancement.

Depending on their careers, Guzzo believes mothers are "right to worry" about being out of the workforce too long. "They feel obligated to try to keep their toes in the water, so to speak, so that they aren't forgotten about or considered as not-good employees," she told Business Insider.

The fertility trade-off

Still, the biggest obstacle to spacing kids out is the fear of waiting too long.

If some mothers have their first child in their early 30s and wait 3 or 4 years, they might be trying for their second child in their late 30s or early 40s, when fertility begins to decline on average. Any money they may have saved on childcare might now go to fertility treatments. IVF, a fertility treatment in which an egg and sperm are fertilized in a lab and the resulting embryo is implanted into a woman's uterus, can cost $15,000-$20,000 per cycle without insurance.

In Darnell's case, the trade-off for waiting was that she had to undergo IUI, a typically cheaper and simpler fertility procedure involving a doctor placing concentrated sperm directly into a woman's uterus, at 37. "Knowing that the clock was ticking, we did go investigate fertility doctors earlier than we probably would have in that process," she said, noting that they would have tried to conceive naturally for longer had they been younger.

Luckily, she said, IUI worked for her in the first round and was covered by her husband's insurance. "We were fortunate in that aspect," she said.

**The perks of an older older sibling**

Beyond giving parents some more financial breathing room, spacing out kids can also make parenting itself a little less chaotic.

Compared to when they're 2, kids who are 3 or 4 are more verbal and generally easier to communicate with. They might also be done with potty training, something both Darnell and Donahue said was a huge help when simultaneously managing a newborn.

Trish Byron-Wilcox, who's the chief of staff for a mineral sunscreen company, has a daughter and son almost exactly three years apart, ages 4 and 1, by the end of this month. The Dallas resident said her daughter being 3 when her son was born made a huge difference in her parenting experience — especially when her husband, who works in industrial distribution, has to travel for up to a week at a time for on-site visits.

The first time she was alone with both kids, she marveled at how easy it was to step away from her daughter to put her baby son to bed, thanks to her daughter's independence. "I was able to just go upstairs with my son and then come back down, and she was happy as a clam," Byron-Wilcox, 36, told Business Insider. "We don't worry about her running away or doing kind of frantic, 2-year-old, toddlery things."

Some parents, like Darnell, are also pleasantly surprised to see that a bigger age gap doesn't stop their kids from being close. "I do feel like my son grasped and understood what getting a baby sister was going to be like when he was a little bit older," she said. "He's a great big brother, and they play now."

Donahue said her children with the 4-year age gap actually get along better than her second and third children with the 2-year gap. Her oldest was old enough to embrace the big brother role, and even help Donahue care for the middle child. But the youngest two just didn't get along as well.

"They started fighting right away because the age difference is so small that they still were interested in the same toys," Donahue said.

As someone who's tried both longer and shorter age gaps, Donahue said there's no doubt in her mind which one she prefers: "I would space them out like that if I could have this last time around, too."

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Julia is a senior health reporter at Business Insider. Julia covers a wide range of topics, including the rise of colon cancer cases among young people, the unique challenges modern parents face, and the growing trend of Gen Zers abstaining from social media. She also writes about fitness, nutrition, longevity, and the routines of highly successful people for Business Insider’s Power Hours series. She’s published interviews with Arnold Schwarzenegger, Serena Williams, Esther Perel, Bill Nye, Naomi Watts, and James Van Der Beek.Julia's work has appeared on the BBC, CBS, Bloomberg Radio, Morning Brew, Fast Company, and the Daily Flash. She has also moderated panel discussions at Nasdaq and Duke University, and appeared on the podcasts Open to Debate, Airtalk, The Evan Bray Show, and The Last Show with David Cooper. Prior to this role, Julia was an education and personal development editor on the Business Insider Reviews team and a sex and relationships editor at Cosmopolitan and BuzzFeed, respectively.You can say hi to Julia at [email protected] and check out more of her work on her website.