GeForce Now is a subscription service to "rent" a video card through Nvidia's data centers. You play games over the internet, with the games running inside their data centers, and the picture is sent back to you. This can be appealing for a number of reasons for many people.

• No scarcity - you don't have to worry about upgrading your computer and fighting scarce video card resources if you simply rent the video card service. It transfers ownership away and puts the burden into Nvidia's hands.
• No upgrading - you can scale up your game library and play newer titles without ever needing to upgrade your years-old computer. A very attractive premise.
• Less power usage - not running a super fancy video card would ideally mean less power used overall in your household. The service is translated from higher electricity costs to higher internet bill.
• More titles for less - asumming Nvidia supplies a steady source of free games occasionally, you are going to be able to play newer titles more consistently without ever having to ugprade your computer itself, and also still be able to access your older game libraries too.

However, the grass may not always be greener on the other side.

• Internet dependency - you need an active internet connection to play your games
• Internet service quality - you need fast download speeds to get higher quality images
• Home location - depending on your distance to an Nvidia data center, you may get slower input response times the higher your net latency is
• Vendor lock - not saying Nvidia is to disappear overnight and leave you stranded, but if the prices go up, what's the competitor in this market?
• Service limits - not all people have unlimited download internet plans
• Compatibility - might only ever work inside Google Chrome or on Windows via a program
• Security - does GeForce Now have proper security measures to make sure you don't get locked out of your game library?
• Invisible Costs - beyond it all sound like magic, is this actually a more cost-effective solution for gaming as a whole?

Those fears aside, some of those are qualitative and nothing can be calculated off that. However, this calculator wants to show you the costs involved of using GeForce Now as opposed to buying a video card and using it on your own. You can punch in your own numbers or use the defaults, but the idea is to give you a baseline estimate over a period of time.

Disclosure: I do occasionally try out GeForce Now on my computer, but only as a means to measure viability. I do not pay for it, nor am I sponsored by GeForce in any capacity. I don't think it's a bad service, but not enough information is public surrounding the true costs of streaming video game platforms.