Definition
A parlay boost is a promotion that increases the payout odds on a parlay. It does not change the chance that each leg wins; it only changes what the ticket pays if every leg wins.
For positive American odds, boosted profit is:
stake × boosted_odds / 100
For negative American odds, boosted profit is:
stake × 100 / absolute_odds
Most parlay boosts are shown as a percentage added to the original parlay profit, so:
boosted_profit = original_profit × (1 + boost_percentage)
Worked Example
A bettor makes a 3-leg parlay with each leg at -110.
Each -110 leg has decimal odds of:
1 + 100 / 110 = 1.9091
Parlay decimal odds:
1.9091 × 1.9091 × 1.9091 = 6.967
A $25 stake would return:
$25 × 6.967 = $174.18
That includes the $25 stake, so the profit is:
$174.18 - $25 = $149.18
With a 20% parlay boost applied to profit:
$149.18 × 1.20 = $179.02 boosted profit
Total payout:
$179.02 + $25 = $204.02
Why It Matters
A parlay boost helps a bettor compare the promoted payout against the true combined price of the legs. It matters most when the boosted payout is large enough to offset the sportsbook margin already built into the parlay.