Odds Calculator API

Overview

The Odds Calculator API helps you determine how many attempts (tickets, tries, etc.) are required to achieve specific probability thresholds of success for events with known odds. Given odds of "1 in N", the API calculates how many attempts you need to have a 50%, 80%, and 95% chance of at least one success.

Endpoint

Request

Headers

Request Body Parameters

Request Example

{
  "odds": 1000
}

Response

Success Response (200 OK)

Success Response Example

{
  "odds_one_in": 1000,
  "attempts_for_50_percent": 693,
  "attempts_for_80_percent": 1609,
  "attempts_for_95_percent": 2996
}

Error Response (400 Bad Request)

Error Response Examples

{
  "error": "Missing or invalid numeric parameter: 'odds'."
}

{
  "error": "Odds must be a positive number."
}

{
  "error": "Invalid or empty JSON input."
}

Mathematical Background

The API uses probability theory to calculate the required number of attempts. For an event with probability p = 1/N of success on each attempt:

• The probability of losing all n attempts is: (1 - p)^n
• The probability of at least one success is: 1 - (1 - p)^n

The API iteratively calculates the minimum number of attempts n where the probability of at least one success meets or exceeds each threshold (50%, 80%, 95%).

Code Examples

JavaScript (Fetch API)

fetch('https://www.promptbox.cn/api/odds.php', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json'
  },
  body: JSON.stringify({
    odds: 1000
  })
})
.then(response => response.json())
.then(data => {
  console.log('For 50% chance:', data.attempts_for_50_percent, 'attempts');
  console.log('For 80% chance:', data.attempts_for_80_percent, 'attempts');
  console.log('For 95% chance:', data.attempts_for_95_percent, 'attempts');
})
.catch(error => console.error('Error:', error));

Python (requests)

import requests
import json

url = 'https://www.promptbox.cn/api/odds.php'
data = {'odds': 1000}

response = requests.post(url, json=data)
result = response.json()

if response.status_code == 200:
    print(f"For 50% chance: {result['attempts_for_50_percent']} attempts")
    print(f"For 80% chance: {result['attempts_for_80_percent']} attempts")
    print(f"For 95% chance: {result['attempts_for_95_percent']} attempts")
else:
    print(f"Error: {result['error']}")

cURL

curl -X POST https://www.promptbox.cn/api/odds.php \
  -H "Content-Type: application/json" \
  -d '{"odds": 1000}'

PHP

<?php
$url = 'https://www.promptbox.cn/api/odds.php';
$data = ['odds' => 1000];

$options = [
    'http' => [
        'header'  => "Content-Type: application/json\r\n",
        'method'  => 'POST',
        'content' => json_encode($data)
    ]
];

$context = stream_context_create($options);
$response = file_get_contents($url, false, $context);
$result = json_decode($response, true);

if (isset($result['attempts_for_50_percent'])) {
    echo "For 50% chance: {$result['attempts_for_50_percent']} attempts\n";
    echo "For 80% chance: {$result['attempts_for_80_percent']} attempts\n";
    echo "For 95% chance: {$result['attempts_for_95_percent']} attempts\n";
} else {
    echo "Error: {$result['error']}\n";
}
?>

Use Cases

• Lottery Analysis: Determine how many tickets you need to buy for a reasonable chance of winning
• Gaming: Calculate attempts needed to obtain rare items with known drop rates
• Quality Control: Estimate sample sizes needed to detect defects with known occurrence rates
• A/B Testing: Determine how many trials are needed to observe events with low probabilities
• Risk Assessment: Analyze how many exposures to a risk factor might lead to an adverse event
• Resource Planning: Plan inventory or resources based on probabilistic demand

Limitations and Considerations

• The calculation assumes independent events - each attempt has the same probability
• This is for calculating at least one success, not multiple successes
• Very small odds (very large N values) may require many iterations and take longer to compute
• The API does not account for external factors that might change the odds over time
• Results are theoretical probabilities and may differ from actual outcomes in practice

Rate Limits and Best Practices

• No explicit rate limits are currently enforced, but please use the API responsibly
• Cache results when possible to reduce unnecessary API calls
• For batch processing, consider adding delays between requests
• Validate input on the client side before making API calls
• Handle both success and error responses appropriately in your application

Support and Contact

For questions, issues, or feature requests regarding this API:

• Visit: promptbox.cn
• Report issues or suggest improvements through the website contact form