• Your estimated fertility window is from ${formatDate(fertilityStart)} to ${formatDate(fertilityEnd)}.
• Your estimated ovulation date is ${formatDate(ovulationDate)}.
• Your next expected period start date is ${formatDate(nextPeriod)}.

To maximize your chances of conception:

• Have intercourse every other day during your fertility window.
• Use ovulation predictor kits for more precise timing.
• Track your basal body temperature and cervical mucus changes.

`; result.style.display = 'block'; updateCycleChart(lastPeriod, ovulationDate, nextPeriod); } function formatDate(date) { return date.toLocaleDateString('en-US', { weekday: 'long', year: 'numeric', month: 'long', day: 'numeric' }); } function updateCycleChart(lastPeriod, ovulationDate, nextPeriod) { const ctx = document.getElementById('cycle-chart').getContext('2d'); if (cycleChart) { cycleChart.destroy(); } cycleChart = new Chart(ctx, { type: 'line', data: { labels: getDates(lastPeriod, nextPeriod), datasets: [{ label: 'Fertility Level', data: getFertilityLevels(lastPeriod, ovulationDate, nextPeriod), borderColor: 'rgba(106, 27, 154, 1)', backgroundColor: 'rgba(106, 27, 154, 0.2)', tension: 0.4 }] }, options: { responsive: true, scales: { y: { beginAtZero: true, max: 100, title: { display: true, text: 'Fertility Level' } }, x: { title: { display: true, text: 'Date' } } } } }); } function getDates(start, end) { const dates = []; let currentDate = new Date(start); while (currentDate <= end) { dates.push(currentDate.toLocaleDateString('en-US', { month: 'short', day: 'numeric' })); currentDate.setDate(currentDate.getDate() + 1); } return dates; } function getFertilityLevels(lastPeriod, ovulationDate, nextPeriod) { const levels = []; let currentDate = new Date(lastPeriod); while (currentDate <= nextPeriod) { const daysUntilOvulation = Math.round((ovulationDate - currentDate) / (24 * 60 * 60 * 1000)); let fertilityLevel; if (daysUntilOvulation >= 0 && daysUntilOvulation <= 5) { fertilityLevel = 20 * (6 - daysUntilOvulation); } else if (daysUntilOvulation === -1) { fertilityLevel = 100; } else { fertilityLevel = 10; } levels.push(fertilityLevel); currentDate.setDate(currentDate.getDate() + 1); } return levels; } });