VPIP (Voluntarily Put money In Pot) is the percentage of hands in which you put money into the pot by choice before the flop: calling, raising or limping. It's the stat that best sums up how loose or tight you play.
How it's calculated
Posting a forced blind doesn't count: if you're in the BB and everyone folds, or you check without putting in more, it doesn't add up.
The healthy ranges on the side are guidelines for NL Hold'em cash games with 100 bb stacks, the same ones Flopmortem compares your game against. Use them to spot big deviations, not as an exact target: they depend on the table, your opponents and your style.
How to read your VPIP
A high VPIP almost always means you play too many marginal hands, especially out of position, and those hands lose money in the long run. A very low one makes you predictable: opponents fold when you enter and your good hands don't get paid.
Always read it together with PFR. The gap between the two tells you how often you get in by calling instead of raising: if your VPIP is 30 and your PFR 12, you call too much preflop, one of the most expensive leaks in low-stakes cash games.
Look at your VPIP by position too: a 25% overall can hide a 20% from UTG (too much) and a 35% on the button (too little). Flopmortem breaks it down seat by seat.
If your VPIP is out of range
Too low
You play very few hands (too tight): you're leaving value on the table. Widen your range in the CO, BTN and SB.
Too high
You play too many hands. Marginal hands out of position lose money in the long run: tighten your ranges from early position and the SB.
How many hands you need to trust it
Flopmortem doesn't flag your VPIP as a leak until it has at least 100 opportunities. From there it calculates it with its 95% confidence interval: if the whole interval falls outside the healthy range, the leak is confirmed; if only the measured value is outside, it's a trend. The guide how many hands you need to trust your stats explains it.