How to Calculate Reading Time: Formulas & WPM Benchmarks

export interface ReadingTimeResult {
  minutes: number;
  seconds: number;
  wordCount: number;
  textBadge: string;
}

export function computeReadingTime(
  content: string,
  imageCount: number = 0,
  wordsPerMinute: number = 225
): ReadingTimeResult {
  if (!content || content.trim().length === 0) {
    return { minutes: 0, seconds: 0, wordCount: 0, textBadge: "0 min read" };
  }

  // 1. Tokenize words stripping HTML tags
  const cleanText = content.replace(/<[^>]*>/g, " ");
  const words = cleanText.trim().match(/[\p{L}\p{N}]+(?:['’\-_][\p{L}\p{N}]+)*/gu) || [];
  const wordCount = words.length;

  // 2. Base word duration in seconds
  let totalSeconds = (wordCount / wordsPerMinute) * 60;

  // 3. Add visual image decay penalty
  for (let i = 1; i <= imageCount; i++) {
    const penalty = Math.max(13 - i, 3);
    totalSeconds += penalty;
  }

  const roundedMinutes = Math.max(1, Math.ceil(totalSeconds / 60));

  return {
    minutes: roundedMinutes,
    seconds: Math.round(totalSeconds),
    wordCount,
    textBadge: `${roundedMinutes} min read`
  };
}