Defending the big blind
In the big blind you have already paid one big blind. That makes calling a raise cheaper for you than for anyone else, and it is why this seat plays the most hands.
The price
Against an open to 2.5 big blinds with the small blind folding, you call 1.5 to win a pot of 4. That needs about 27% equity, before counting that you will be out of position.
Being out of position means you collect less than your raw equity, so the price is a guide and not a licence to call everything.
How wide, by opener
The opener’s position decides your range. In the starting charts: against UTG, call 16% and raise 3%; against HJ, call 20% and raise 5%; against CO, call 26% and raise 7%; against BTN, call 43% and raise 11%; against SB, call 37% and raise 15%.
Against an early-position open you face a strong range and continue tightly. Against the button and the small blind you face a wide one and defend much more.
After the flop
You act first, usually against the player who raised. The standard plan is to check to the raiser, call with hands that can stand a bet, and use the check-raise with your strongest hands and best draws.
About the numbers
The figures come from the rule-of-thumb charts on this site, not from a solver. In the trainer you can edit every chart and train on the hands at the edge of the range.
The charts
Work it out
Terms in this guide
Practise it
Reading is the easy part. Play the hand of the day, or deal ten hands in the trainer and see which of these decisions cost you the most.