Have you ever wondered what your life (or your bank account) would look like if you’d invested in Apple or Facebook early on?

This new online calculator lets you kick yourself (or breathe a sigh of relief) by instantly figuring out how much money you would have made or lost in the stock market.

Developers Shivkanth Bagavathy and Jordan Gonen rolled out ExtremeFOMO.com on Monday at midnight, so named because they say the most extreme fear-of-missing-out is the financial kind. The application program interface (API) was inspired by WhatifBitcoin, which calculates what you would have made by investing in BitCoin on various dates.

ExtremeFOMO invites you to pick a company, enter how much you would have invested and when. So if you bought into Facebook with $1,000 on its initial public offering (IPO) on May 18, 2012, for example, you learn you would’ve made $2,969.32, or a 363.93% return on investment (ROI.)

ExtremeFOMO.com lets you see what your investments could have been. (screenshot)

But if you would have dropped a grand on Snap when it went public last March, you would’ve lost $383.33 as its stock has sunk.

“People’s biggest fear, especially in today’s world, is missing out on things, and it’s human nature to get jealous of other people’s finances or what they’re posting on social media,” co-creator Gonen told Moneyish. “So we just decided it would be fun to build something over the weekend to see how investing works.”

He says the calculator has clocked about 10,000 uses already, with most people playing with the randomized generator that shows what you would have lost or gained by backing hip brands like Tesla, Amazon, Google, Apple and Alibaba. The default date is set at Jan. 1, 2014, although the application automatically tweaks the date if the IPO launched after that. It goes back to 2002, Gonen said.

ExtremeFOMO.com lets you see what your investments could have been – like earning almost $17,000 by investing in Tesla early on. (screenshot)

“It’s just cool to see,” he added. “Anyone can invest, but it does take research, skill and money. So this grounds that, and shows that if you’re confident in what you’re doing, and have conviction, there’s the potential for a big payoff – or, there’s also a big downside.”

Here’s some of the winners and losers on ExtremeFOMO.com:

Tesla:

Investing $1,000 in June 2010 would have made you $16,867.37 – or a whopping 1,786.74% ROI. Even waiting until January 2014 would’ve earned $1,266.22 by now.

Apple:

Early birds who invested $1,000 in Apple on Jan. 1, 2002 would’ve made $6,260.77 – but if you waited until Jan. 1, 2014, you lost $711.88.

Yelp:

Investing $1,000 on March 2, 2012 would’ve made $921.40, but those waiting until January 2014 lost $384.87.

Google:

Buying in with $1,000 in August 2004 could’ve earned an extra $8,198.58, but waiting for January 2014 would’ve cost investors $188.59.

Twitter:

Dropping $1,000 when it went public in November 2013 would’ve cost $631.71, and it’s only continued to drop.