Preflop is where GTO study pays off fastest: the decisions repeat every orbit, the spots are few, and the ranges can be memorised. It's also where small habits leak the most, because a preflop error repeats thousands of times. These are the seven preflop range mistakes we see most often, and the fix they share.
1. Copying the chart without knowing why
A solver gives you an answer, not an understanding. If you memorise that a hand raises without knowing why it raises rather than calls, you'll misapply it the moment one variable changes: a different open size, a shorter stack, an ante. For every region of a range, be able to say what makes it play that way: blockers, playability, equity against the continuing range.
2. Using the wrong format's ranges
A 100bb 6-max cash chart is the wrong reference for a 20bb Spin & Go or a 30bb tournament with antes. Ranges shift hard with format:
| Factor | Effect on preflop ranges |
|---|---|
| Shorter stacks | Fewer flats, more jams and min-raises; hands with good equity gain, small suited hands lose |
| Antes | Bigger pot to win, so wider opens and much wider big blind defence |
| Higher rake | Tighter, fewer thin flats and limps, more 3-bet or fold |
| Fewer players | Wider everything, since fewer players are left to wake up with a hand |
| ICM pressure | Tighter calling ranges, more pressure from the bigger stack |
Check that the solution matches your format, stack depth and rake before learning it. More on this in how accurate GTO solutions are.
3. Over-fitting to one stack depth
Players build a beautiful 100bb strategy and then play a session where half the table sits at 40bb. If you play tournaments or Spins, the stack changes every few hands. Know which depths you've actually studied, and learn the direction ranges move as stacks shrink, not just one snapshot.
4. Building ranges you never drill
A range you built once and filed away is not knowledge you own. If it's not in your drill rotation within a week, it won't be there when the spot comes up. Recall, not recognition, is what holds at the table. See the GTO trainer study routine.
5. Learning opens but not the response to 3-bets
Most players can recite their button open and then guess when it gets 3-bet. Every opening range needs a matching plan: which hands 4-bet, which call, which fold. Without it, a wide open range becomes a liability.
6. Treating "mixed" as "random"
When a hand plays two actions at some frequency, that's a signal about how close the decision is, not permission to guess. Mixed hands sit on a boundary. Understand what puts them there and you'll read the whole region of the range better. And remember the priority: getting pure hands right matters far more than nailing a 60/40 mix.
7. Ignoring the big blind
The big blind is the position you play most hands from and lose the most money in; that's normal, since you've already paid a blind. The leak is defending too tightly. You're getting a good price against small opens, so the GTO defence range is wide. See BTN vs BB and SB vs BB.
The fix is the same each time
Slow down at the point where you'd normally copy an answer and make yourself state the reason. If you can't, that's the spot to study next. Then drill it until the answer is automatic, and check your real hands to find the leaks that remain.