I have been trying to understand how AWS Reserved Instances works exactly reading AWS documentation and looking on Google but could find literal information about my concern.

Reading this (Reserved Instances » How You Are Billed) I understand that, hour based you can have 4 instances running 15 minutes and they will use a full hour from 1 reserved instance.

But if we have one Reserved Instance, what gives us 24h a day, if we have 4 instances running only 6h a day concurrently, will they use the 24h given by the Reserved Instance? Or will only one will use 6h and the other 3 instances will be billed as On Demand?

Thank you in advance.

1 Answer 1


6h of reserved usage, the rest on demand.

A "budget" of 3600 seconds of reserved usage that resets every clock hour. So technically 4 instances burned through the reserved hour 15 minutes in.

It is a compromise that rewards continuous usage, but also acknowledges that concurrent use exists.

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