Period Calculator
Predict your next period dates and cycle phases over the coming months.
Period Calculator
Predict your next period dates and cycle phases over the coming months.
Pregnancy Due Date — Naegele's Rule
ℹ️ Only 5% of babies are born on their exact due date. Dates are estimates only.
Disclaimer
Results provided by this calculator are for informational and educational purposes only. They are based on the values you enter and standard formulas, and should not be considered financial, medical, legal, or professional advice. Always consult a qualified professional before making important decisions based on these results. Roughtools makes no warranties regarding the accuracy or completeness of these calculations for your specific situation.
Frequently Asked Questions
Pro Tips
Only about 5% of babies are born on their due date — the Naegele's Rule date is the midpoint of a 5-week window. Don't over-plan for the exact date.
Early ultrasound (6-10 weeks) is more accurate for dating than last menstrual period if your cycles are irregular. Your OB may adjust your due date based on ultrasound.
Gestational age in weeks is counted from LMP, not conception. "6 weeks pregnant" means 6 weeks since your last period, which is only 4 weeks since likely conception.
Track your symptoms week by week using the trimester milestones. Many pregnancy apps let you export a report — useful to share with your healthcare provider.
When to Use This Calculator
Calculate your due date to plan maternity leave timing, financial preparation, and childcare arrangements.
Calculate your estimated due date in advance so you can ask the right questions at your first OB appointment.
Know your due date to schedule the baby shower at the right time — typically 4–6 weeks before delivery.
Share your due date with family and friends as a planning tool, while reminding them only 5% of babies arrive on that date.
Parents of multiple children often plan birth timing around school enrollment cutoffs — use the due date to estimate.
About the Period Calculator
The Period Calculator predicts future menstrual period start dates for the next 12 months based on your last period date and average cycle length. It shows the expected start date, period duration, and the days until each period. Use it for cycle tracking, appointment scheduling, event planning, or before starting a new form of birth control.
How to Use the Period Calculator
- 1
Enter the start date of your last period.
- 2
Enter your average cycle length (21–35 days; 28 is typical).
- 3
Optionally enter your average period duration (3–7 days).
- 4
Click Calculate to see the next 12 predicted period dates.
- 5
Save or export the schedule for your calendar.
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Due Date Calculator
Calculate pregnancy due date from last menstrual period or conception date.
Conception Calculator
Estimate your most likely conception date based on your due date or LMP.
Pregnancy Calculator
Calculate pregnancy week, trimester, and key milestone dates.
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