User Guide: Closing Line Value (CLV) Calculator

What this does

• Compares the odds you bet to the market’s closing line.
• Shows how much you “beat the close” using implied probability, plus optional EV and price-change views.

How to use

1. Choose your input format:
   • American: enter the absolute number (e.g., 110) and select the sign (- or +).
   • Decimal: enter the decimal (e.g., 1.91).
   • Fractional: enter the fraction (e.g., 10/11).
2. Select “Back” (typical sportsbook bets) or “Lay” (exchange lay bets). The main calculation uses back perspective; lay is for context.
3. Enter:
   • Your bet (opening): the odds you took.
   • Closing line: the market’s final odds.
4. Click Calculate.

Understanding the results

• Implied probability (your bet): Probability implied by your odds. For decimal odds d, p = 1/d.
• Implied probability (closing): Probability implied by the closing line.
• You beat the close by: (p_close − p_open) / p_close
  • Positive = you got a better price than the closing line.
  • Negative = you got a worse price than the closing line.

Advanced metrics (in the “Show advanced metrics” section)

• Decimal odds (yours / close): Your odds vs the closing odds in decimal format for easy comparison.
• Price change (sign-aware): A quick relative difference in American-odds terms.
  • Favorites (negative odds): less negative is better for backers.
  • Underdogs (positive odds): more positive is better for backers.
  • If the sign flips (from + to − or vice versa), it will show both prices for clarity.
• EV edge vs close (per $1 staked): Expected value of your bet assuming the closing line reflects the true probability.
  • Positive = theoretically +EV vs close.
  • Example: +0.0123 means +1.23 cents per $1 stake.

Tips and notes

• This compares single-side implied probabilities and includes vig. If you have both sides of a two-way market, you can de-vig separately (not covered here).
• Enter clean numbers:
  • American format expects a number in the box (e.g., 110) and you choose + or − with the buttons.
  • Decimal must be greater than 1.00.
  • Fractional must be a valid fraction like 10/11, 5/6, 7/5.
• “Back” vs “Lay” doesn’t change the core probability formula; it’s provided for context if you’re using exchanges.
• For favorites, a movement from -110 to -118 means the closing line got worse for backers; if you bet earlier at -110, you “beat” the close.
• For underdogs, a movement from +150 to +140 means the closing line got worse for backers; if you got +150, you “beat” the close.

Common examples

• You bet -110, close is -118:
  • p_open = 110 / (110 + 100) ≈ 52.38%
  • p_close = 118 / (118 + 100) ≈ 54.13%
  • Beat % ≈ (54.13 − 52.38) / 54.13 ≈ 3.23%
• You bet +150, close is +140:
  • p_open ≈ 100 / (150 + 100) = 40.00%
  • p_close ≈ 100 / (140 + 100) ≈ 41.67%
  • Beat % ≈ (41.67 − 40.00) / 41.67 ≈ 4.00%

Troubleshooting

• If the Calculate button does nothing, ensure both odds are valid and greater than 1.00 in decimal terms.
• If using a CMS that auto-formats code, the app provided avoids operators that often get mangled. If issues persist, host the JavaScript in an external .js file and include it with a script src tag.
• Reset clears inputs and restores defaults.