It varies a lot depending on a few variables:
- Which client and which version of the client you are using.
- How many peers you are connected to.
- If your machine is configured correctly to accept incoming connections.
- How many resyncing nodes you are connected to.
It will likely amount to something between 500 GB and 3 TB of combined download and upload per month.
I've been recommending 4.5 MB/s up and 4.5 MB/s down for your bandwidth needs if you are running an eth1/execution client and an eth2/consensus client (that's 36 mbps up and 36 mbps down) which is somewhat aligned with the documentation on https://ethereum.org/en/developers/docs/nodes-and-clients/ but many people have been able to run it with much lower bandwidth allowance. That recommendation should be good for usage peaks.
You could tweak and lower the amount of connected peers with your clients to lower the bandwidth usage but I would not suggest doing so. The default number of peers should be a baseline value for normal operation.