Using bitcoin-cli, how do I check how sync'ed my full node is?
getblockchaininfo is your best bet. It includes a field called
verificationprogress, which is an estimate of how much of the chain you have validated.
headers is higher, it means that your node has validated the headers for blocks that it has yet to validate. When these numbers match up, it either means you are up to date, or for some reason your node isn't receiving any more block headers. Unfortunately, this doesn't tell you how much further you have to go, since
headers may be well behind the rest of the network. You can always compare these values to those provided by an online block explorer. Still, when these numbers match (or are 1 apart), it generally means you are synced.
There are also some good suggestions on this question: How to know if bitcoind synced?