What the calculator does
It answers one question: is the price you can get better than the price the bet is really worth? The bet's real worth is its fair odds, the odds you'd get if the bookmaker took no margin at all.
Pinnacle is a bookmaker known for very small margins and prices that move quickly when sharp bettors act, so its line is the best available estimate of the true probability. Enter Pinnacle's odds for every outcome, and the calculator removes its margin to get the fair chance.
A worked example
Pinnacle offers 2.05 on your bet and 1.85 on the other side. Those add up to more than 100% (102.8%): the extra is Pinnacle's margin. Removing it with Shin's method leaves a fair chance of 47.4%, which is fair odds of 2.11.
Your bookmaker offers 2.30. Expected value is 2.30 × 47.4% − 1 = +8.9%: on average you make 8.9 for every 100 staked, over many bets. Half Kelly suggests about 3.4 units.
Reading the numbers
Expected value is the average profit per unit staked if the fair chance is right. It is small per bet, which is why only a long series of bets shows it.
Half Kelly is the stake that would grow a bankroll fastest if the estimate were exact, cut in half because estimates never are. Sharp Bets uses it and expresses stakes in units of 1% of the bankroll.
Shin or proportional? Proportional spreads the margin evenly over the outcomes. Shin assumes some of it is there to protect against informed money, which makes long shots look slightly less likely. The two agree on even markets and differ on lopsided ones.
Limits
The result is only as good as the fair odds. Pinnacle's line is very good but not perfect, and it is a snapshot: odds keep moving until kickoff. Always check the price at your bookmaker before betting.