The Hobby plan's $5 is not a one-time credit like the trial. It includes $5 of resource usage every billing cycle, meaning if your services consume $5 or less per month, you only pay the $5 subscription fee. If your usage exceeds $5 in a month, you pay the overage on top. Whether $5/month is enough depends on how many services you run and how much CPU/memory they consume. The same applies to the Pro plan, which includes $20 of usage per month. You can see full pricing details at railway.com/pricing.

While my services used $5 in 10 days with the free plan, does it mean that it will use $5 in the Hobby plan in 10 days as well?

Yes, if your services consume resources at the same rate, the $5 included usage on the Hobby plan would be used up in roughly 10 days as well. The difference is that on the Hobby plan your services keep running and you pay for any overage beyond $5, whereas the trial simply ends. If you want more included usage, the Pro plan includes $20/month. You can also reduce costs by enabling app sleeping on services that don't need to run 24/7, or by reviewing which services are consuming the most resources.

how much do you think a medium business app will cost in a month. suppose a medium management app built with react, nextjs, prisma, mysql and nestjs. the app has 5 users daily.

Hey, this totally depends on the resources that your application needs and not really by the amount of users. With that being said, I would estimate the usage to be in the range of $10 to $20 when run 24/7, as all of your services don't seem to be particularly memory friendly (in fact, they are all a bit memory hungry, you may want to consider alternatives such as using Golang instead of NestJS and MariaDB instead of MySQL). As mentioned above you want and perhaps should enable serverless/app sleeping to reduce your usage, as you don't have a lot of users yet.

Thank you for the advice