Women's Health
Use this menstrual cycle calculator to calculate estimate next period date, ovulation date, fertile window, and cycle timeline from the last period start date.
Calculator
Cycle estimate
2026-08-18
Expected next period date based on the average cycle length you entered.
Expected next period
2026-08-18
Approximate ovulation
2026-08-04
Fertile window start
2026-07-30
Fertile window end
2026-08-05
Period starts
Fertile window
Ovulation
Next period
Sign in to save this calculation and access it later.
Trust note
This calculator is informational and should be verified before financial, health, legal, engineering, laboratory, or safety-critical decisions.
Next period = last period start + average cycle length
This calculator applies the formula Next period = last period start + average cycle length. Enter each value with the matching unit, and AZCalculate updates the result instantly.
Assumptions
Avoid mistakes
Follow the reasoning, not only the final number.
Enter the known values in the calculator fields.
Starting with clearly defined values and units prevents the most common calculation errors.
Keep the units consistent with the labels shown beside each input.
This step transforms the known values into the form required by the formula.
Apply the formula: Next period = last period start + average cycle length.
This step transforms the known values into the form required by the formula.
Review the primary result and supporting values.
Compare the result with your real-world goal, such as estimate the next period.
Worked example
Days until next cycle: 28 days
Calculator guide
Estimate next period date, ovulation date, fertile window, and cycle timeline from the last period start date. This page includes an interactive calculator, concise formula notes, worked examples, FAQs, related calculators, and practical guidance you can revisit whenever needed.
References
We work hard to keep every calculator accurate and useful. If you notice a calculation error, missing option, or unclear explanation, please let us know so we can review and correct it promptly.
Usage information loads after the calculator is ready.
FAQ
It uses Next period = last period start + average cycle length and calculates the result from the values you enter.
Yes. AZCalculate calculator pages include copy, share, and print actions.
No. They are estimates based on dates and average cycle length.
No. Speak with a qualified healthcare professional for medical concerns.
Use it as an estimate and compare it with the formula, assumptions, and examples shown on the page.
Real-world inputs can include local rules, changing rates, measurement tolerances, and conditions outside the core formula.
Enter the known values requested by the calculator. Use the unit selectors where available and make sure the values describe the same scenario.
The calculator follows the formula shown on this page. Accuracy depends on the values, units, assumptions, and rounding used in your scenario.
Related tools
Continue with closely related tools selected from the same subject and matching calculation needs.
Estimate upcoming period dates from your last period start date, cycle length, and period duration.
Estimate ovulation day from cycle length and luteal phase.
Estimate fertile window and approximate ovulation date from cycle timing.
Estimate days to due date from current pregnancy week and day.
Estimate bra band size, cup size, full size, sister sizes, and fit guidance from band and bust measurements.
Estimate travel costs for transport, accommodation, food, activities, and business expenses, then see total trip cost, cost per person, cost per day, budget health, and savings guidance.
Estimate notice-period end offset using calendar days, working-day adjustment, and handover buffer.
Estimate Shopify-style selling and payment fees using your own entered percentage rate, fixed fee, and plan cost assumptions.
