When to Split 10s in Blackjack

The answer: never split 10,10

Basic strategy says to stand on every pair of ten-value cards against every dealer upcard. That includes 10,10, J,J, Q,Q, K,K, and mixed ten-value pairs if the casino allows them to split.

Why 20 should stay 20

A hard 20 wins most of the time against every dealer upcard. Splitting it creates two hands starting at 10. Those are good starts, but they are not better than keeping the original 20. You are giving up a strong made hand to chase two uncertain hands.

What about dealer 5 or 6?

Dealer 5 and 6 are weak, but that does not make splitting 10s correct. Standing on 20 already crushes those dealer cards. Splitting adds volatility and lowers expected value.

Why card counters sometimes split 10s

Advanced card counters can split 10s in very high true counts because the remaining deck is unusually rich in ten-value cards. That is not basic strategy. If you are not tracking the count accurately and using index plays, do not split tens.