How much should you spend on your wedding? Here's what Kevin O'Leary and Ramit Sethi say

Kevin O'Leary vs. Ramit Sethi: Are weddings worth the splurge?

Engagement season is in full swing, which means wedding planning has begun. And it's no small endeavor: In 2017, the average national cost of a wedding was $33,391, according to The Knot. But is it smart to spend that much?

Here's what personal finance experts say when it comes to budgeting for your wedding.

Kevin O'Leary says be frugal and invest the money instead

Instead of blowing thousands of dollars on a party, finance expert and star of ABC's "Shark Tank" Kevin O'Leary says you should invest that money to plan for your life with your significant other.

For example, if you invest that $33,319 that's spent on the average wedding, at a return of 9 percent (the average annualized return for the S&P 500 index over the past 90 years is over 9 percent), by your 10-year anniversary you would have over $79,000, according to an SEC calculator.

O'Leary himself had a low-cost wedding in the '80s when he married his wife, Linda.

"I said to my wife, 'Why go in debt?' Let's invite our friends over, let's buy a few cases of beer and I'll order some pizza," O'Leary tells CNBC Make It.

Kevin O'Leary and his wife, Linda, on their wedding day more than 25 years ago.
Courtesy of Kevin O'Leary

O'Leary says he took the money he saved on his wedding and put it into his business. That worked out well for that couple, as O'Leary now owns multiple businesses and is a self-made multi-millionaire.

"Forget about spending a fortune, you don't need a white dress for $22,000," O'Leary says. It might sound romantic, but it's just not smart, he says.

"Save your money, invest it and later you can take everybody out for a great time on the interest you're making off your bonds and the dividends your stocks are paying."

Sethi says you can spend big, but plan for it

Self-made millionaire and author of "I Will Teach You to be Rich" Ramit Sethi, recommends an entirely different approach to wedding planning.

"Let's be honest," Sethi says. "It's your one special day....You want the nice flowers or the nice chair or the nice chicken. Why not? It's your one day," Sethi tells CNBC Make It. "My advice to you is acknowledge it, plan for it, don't delude yourself into thinking that you are only going to spend $16 on a wedding."

Sethi, 36, who was married in July, had been saving for his wedding since he was 24-years-old, years before he even met his wife, Cassandra. (Sethi notes that Indian weddings are traditionally extravagant, so he knew he'd need a small fortune.) For years he stashed money into a wedding savings account and even had a separate allotment for an engagement ring.

Ramit Sethi with his wife, Cassandra, and their wedding guests.
Source: Ramit Sethi

So by the time he needed to start budgeting for the actual event, Sethi had a pretty clear idea of what he could afford.

"As someone who [has] planned a wedding for over 230 people, and who knows what it takes to save and plan, just be honest with yourself..." Sethi says. "You're probably going to spend more than you think.

"Plan for it, build that [savings] account right now, get on the same page with your partner, make sure you have a vision for what that wedding is."

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Disclosure: CNBC owns the exclusive off-network cable rights to "Shark Tank."