There is a saying that the house always wins. Bookies hold to this first and foremost when calculating odds, meaning they first set their own margin (the profit they’re taking either way, which is usually a certain relatively low percentage). They calculate the odds of something happening either way, then they subtract that margin (also called a vig, vigorish, or juice) and post the odds. The majority of odds are calculated through past events and professional opinions, and many new football betting sites use specialised software for this. The odds also move in response to betting—if one outcome is the more popular one and more people bet on it, the bookie will increase their margin there and decrease the margin on the less popular option, to encourage people to move towards the other option. But if the higher margin odds remain more popular, the bookie still gets their profit. Another popular way to get people to bet on less popular options is through football free bets, as many of them are restricted in a way that they can only be used on higher odds.