Tools · Calculator
Double Down Bet
When the market moves against a live bet but your model still sees value, this sizes the follow-up. Enter your original bet, the new live price and your updated model — it returns the Kelly-sized amount to add and your blended position.
Original Bet your pre-game position
New Opportunity the live price now on offer
Bankroll how the stake is sized
How the double down works
A live line can drift further than the game state justifies. If your updated model still beats the new implied price, the follow-up bet is +EV — and Kelly tells you exactly how much to add.
Why double down
Markets overreact to swings — an early deficit or a first objective. If the price moves more than your model does, your edge grows. The Lakers drop from 48% to 42% in the model, but the market reprices from 40% to 31%, so the value is bigger than pre-game.
Edge model − implied
The new price implies a break-even win rate (implied probability). Subtract it from your live model probability. Positive means the bet is +EV and worth adding to; zero or negative means pass.
Kelly stake (b·p − q) ÷ b
Kelly sizes the new bet from your edge and the price: b is net decimal odds, p your model probability, q = 1 − p. The result is a fraction of bankroll. A fractional multiplier (½, ¼) trims variance — most bettors never stake full Kelly.
Combined position
Both bets ride the same outcome, so the slip blends them: total at risk, the blended odds across both legs, profit if it hits and the full amount lost if it misses. The combined EV is valued at your latest live model.