Everyone knows that for couples and their families, planning and staging a wedding involves serious money.

What generally goes unaddressed is the ever-growing expense faced by those invited to the long string of bachelor and bachelorette parties and bridal showers, never mind the wedding itself.

“The biggest expense I’ve had,” said Shani Silver, 33, referring to these satellite events. Like so many others in her generation, a complicating factor for Silver, who is single and about to start a job as director of digital content at Domino magazine in New York, is that she is still paying off law school debt. Because of that, she said she has to match her social activities to her available budget.

Last spring she paid for two sets of plane tickets to Chicago, first to attend her best friend’s bridal shower and then for an engagement party with a scavenger hunt theme. She also managed to attend this same friend’s wedding in New Orleans.

But Silver had to say no to two other weddings that spring because she had no money left.

She’s far from alone in having to judiciously pick which events to attend. And the costs of doing so are still mounting. A study commissioned by American Express released in April found that the average cost to regular guests of attending only the wedding portion is now $673, compared with $339 in 2012.

Travefy, a website that helps organize group travel, has found a 36 percent increase in spending on bachelorette parties over the course of a year.

David Chait, the chief executive and a founder of the site, said that while the median bachelorette party has seven participants, there is a trend toward larger and larger groups. And among the site’s customers, the average length of a bachelorette party has grown to three days.

While Silver was happy to attend her best friend’s special occasion, she took issue with the idea “that your engagement deserves a party,” she said. “I think your engagement deserves a ring, but you have the biggest party of your life coming up in a year. Why do you have to have one now?”

People are now “over-celebrating” their life events, she finds. And, she asked, how did what was once a party become a “bachelorette weekend”? “And don’t get me started on gifts. Your gift is your husband and your family.”

It’s easy to blame this stress on the narcissism of the bride and groom. The millennials “now are the most entitled generation I have ever seen,” said Maggie Baker, a married psychologist in Wynnewood, Pennsylvania, who has two sons and a nephew who are all now being invited to weddings. “They are all in that age range, so it’s coming at me from all sides.”

Baker, whose practice focuses on financial issues, said that those with financial means sometimes do not think about those who may not be able to afford to attend a bachelorette blowout in Mexico or Paris, or the wedding itself. “It’s not that the bride doesn’t have empathy; she doesn’t use it,” she said.

Some brides validate themselves with external factors like parties and gifts, Baker said; anything less than a big event can be a blow to their self-esteem.

Brides, especially, can and often do feel deserving of a lush event.

“There is this sense of entitlement,” said Kate Kaplan, a married psychologist in Los Angeles who specializes in therapy for brides. “There is this self-centered view that it’s all about me, and everybody is going to make it work.”

Kaplan often hears stories about someone who lost a friend over something wedding related, she said. “Brides are not at their most sort of coherent emotional state,” she said, “so it makes it difficult for them to hear things.”

Stefanie O’Connell, a former actor who is living with someone, is among many in their 20s and 30s feeling financial pressure over attending elaborate and demanding festivities that lead up to and also include the wedding.

She recalled a dispute over a bachelorette party bill that didn’t end a friendship, but left her feeling terribly uncomfortable. To avoid busting her budget, she sought to opt out of the parts of a friend’s bachelorette events that she couldn’t afford. But when her return travel arrangements fell apart, she was forced to stick it out, which left her in the unenviable position of asking her friend to temporarily help pay her portion of the bill.

It’s not that she doesn’t want her friends to celebrate how they please. If they desire three engagement parties or a last festival in Puerto Rico, said O’Connell, now 28 and a writer in New York, “Go do what you want to do and have a blast.” But she doesn’t want the pressure or expectation to participate, which she so often feels, or the fear of losing a friend if she declines.

When O’Connell added up what her friends’ celebrations have been costing her, she said she found the following: “Every wedding is now at least five expensive occasions, each one a minimum of a $100 commitment. I have to go to four or five weddings a year. That’s five times $500, so $2,500 a year. And that’s on the low end, to be quite frank.”

But why don’t guests say no?

A 31-year-old single man, who works in finance in New York City, and asked to remain anonymous to protect his friendships, said: “You don’t want to be the jerk in the group that’s like, ‘No, we aren’t paying for it,’” referring to the two engagement parties, a wedding, a bachelor party and a surprise 30th birthday party he had been asked to attend.

For him, the bigger concern was the amount of time off from work required to go to these events, two of which were out of the country. He justified taking off all of this time, he said, by concluding, “It’s an event centered around happiness and there are a lot of emotions and feelings involved, and for you to push back, you don’t want to disrupt that.”

For her part, Silver still laments missing a wedding of a close friend because she couldn’t afford to attend. “I should have been there,” she said. “I should have seen her get married. I love her and her husband. They are an amazing couple, and I will always wish I was there.”

In the end, she said it was just too much. “I could either not afford my own life, my own rent and celebrate my friends’ happiness, or I could say my day-to-day matters more than your big day.”

But there are some couples who are aware of their friends’ concerns and take that into account when planning a wedding.

Katie Korf of Lebanon, who is 29 and is getting married in March 2016, recognized that her guests, who are split between the East Coast and Utah, may have a hard time attending multiple events.

She decided not to have an engagement party, she said, “because we knew it would be extra money for people.” But she is having a bachelorette party for her closest friends. Korf, a health coach with Omada Health, a San Francisco-based company that advises people on living healthier lives, said she picked Philadelphia because it is a short and cheap train ride for those involved.

She has also worked hard to get a great hotel rate and to arrange shuttles so guests would not need rental cars.

She also wanted to limit other costs for her bridesmaids. She chose dresses from J. Crew from last season that were half price. “ I think they came out to $109, which I was so happy about,” she said. “I’m really trying.”