The reference market
Everything starts with a reference price: the best available estimate of an outcome's true probability. We use the sharpest market, one with low margins, high limits and prices shaped by professional money, and read its prices through a professional odds feed. Recreational bookmakers don't make good references: their prices carry more margin and follow the sharp market with a delay. That delay is what alerts exploit. More in sharp vs soft bookmakers.
From odds to fair odds
A bookmaker's prices add up to more than 100% because they include its fee. Removing it gives the fair probability and the fair odds. BetTheDrop uses the power method: it finds the exponent k such that the probabilities, each raised to k, add up to exactly 100%.
p(i) = q(i)^k where q(i) = 1 ÷ odds(i) and Σ p(i) = 1
We use it instead of the simple proportional (multiplicative) method because bookmakers put more margin on long shots (the favourite–longshot bias). A proportional split leaves long shots with too high a probability and makes value appear that isn't there. Example at odds of 1.25 and 4.20: proportional gives the long shot fair odds of 4.36 and the power method 4.685. You can compare both in the no-vig calculator.
What counts as a drop
- We watch the reference market's prices all day for the main lines (moneyline/1X2, handicaps, totals and team totals) across 13 sports, for the full game and by period where the market offers them.
- A drop is a fall in a price of at least a threshold. By default alerts are drops of 15% or more; on Pro you set your own filters by sport, market, drop size, odds range and period.
- Pre-match only. Live prices move with the game itself, so a live drop usually isn't information.
- Alternative lines of the same market that moved at the same time are grouped in one message: one bet per message.
Drop % = 1 − new odds ÷ old odds
What an alert tells you
Each alert shows the match and kick-off, the market and period, the exact selection, the price before and after the drop, the fair price now and the market's maximum stake. The rule is always the same: bet only if your bookmaker pays more than the fair price. See the guide to reading an alert.
How we measure alerts
- Every alert is stored when it's sent, with the price available before the drop.
- A few minutes before the match starts we read the reference market again for the same selection: that is the closing price, and removing its margin gives the fair closing price.
- The alert's value is the price before the drop against the fair closing price: price ÷ fair close − 1. That is the closing line value (CLV), counted at 1 unit per alert (and at 10 € per alert in the euro figures).
- Alerts are counted once their match has started and the closing price has been read. None are left out because they performed badly.
The results page shows the last 30 days, updated every hour. We publish them as expected value, never as winnings: alerts are not settled against the final score and no stake is actually placed.
Expected value against the fair closing price, not actual winnings: you can lose money even on +EV bets. How we measure it.
What the numbers don't tell you
- They are expected value, not profit. Individual bets vary a lot and you can lose money on +EV bets.
- It's the price before the drop. Your real edge is the price you actually get at your bookmaker against the fair close, often smaller and sometimes zero, which is why every alert shows the fair price.
- The fair price is an estimate. It comes from the best market there is, but it can be wrong.
- Past results don't guarantee future ones.
Independence
BetTheDrop is odds analysis software. It isn't a bookmaker, doesn't accept or place bets, doesn't hold customer money, doesn't sell tips and earns no affiliate commissions from bookmakers: its business model is subscriptions. See the legal notice and responsible gambling. Gambling is for adults (18+).