What is a sports bet calculator?

What it works out

Bet	Wins	Returns, stake included	Has to win
$50 at +150	$75	$125	40 percent
$50 at -120	$41.67	$91.67	54.55 percent

You can do both by hand. The calculator is quicker, and it doesn't make mistakes with minus prices, which is where people slip (I've watched grown men get -120 backwards at a counter).

The four we have

• The odds calculator. Payout and break-even for one bet, with the price shown in American, decimal and fractional form.
• The parlay calculator. What a ticket pays when the legs are multiplied together, so you can check the book's figure.
• The hedge calculator. How much to bet on the other side to lock in a result when a ticket is still alive.
• The no-vig calculator. Takes the book's cut out of a two-sided price and shows the fair odds underneath.

The mistake people make

A calculator tells you what a bet pays. It does not tell you whether the bet is any good.

Most people read the payout and stop, when the figure to read is the break-even: if the calculator says 54.55 percent, the question is whether your side wins more often than that, and no calculator can answer it. I'd read that number first, every time.

The second mistake is with parlays. The payout looks large because the calculator shows what the book pays, and it doesn't show what a fair price would have been. On a five-team parlay at -110 a leg, the book keeps about 20.8 percent.

I'd also run the no-vig calculator on both sides of a game, because it shows you what the book thinks the true chances are, which is worth knowing before you disagree with it. And enter a stake that fits your bankroll, 1 or 2 percent of it, and leave it there. Don't work backwards from the payout you would like.

A calculator gets the sums right. The opinion is still yours.