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Ovulation / Fertility Calculator
Estimate ovulation date, fertile window and next period from last menstrual period, cycle length and luteal phase.
Live math canvas
Your numbers, formula and explanation together
Ovulation / Fertility Calculator: 2026-06-15. Estimated fertile window 2026-06-10 to 2026-06-15. Next period estimate 2026-06-29 from 28-day cycle and 14-day luteal phase.
Formula applied
The exact method behind this answer
CalculationTime keeps the method visible so the number can be checked instead of blindly trusted.
Next period = LMP + cycle length. Estimated ovulation = next period − luteal phase. Fertile window = ovulation − 5 days through ovulation day.
Apply the formulaNext period = LMP + cycle length. Estimated ovulation = next period − luteal phase. Fertile window = ovulation − 5 days through ovulation day.2026-06-15Estimated fertile window 2026-06-10 to 2026-06-15. Next period estimate 2026-06-29 from 28-day cycle and 14-day luteal phase.
Your live breakdown
Current inputs in the calculation
These values come from the controls above and update when the calculator changes.
LMP year
2,026
LMP month
6
LMP day
1
Cycle length
28 days
Luteal phase
14 days
Resulting answer
2026-06-15
Estimated fertile window 2026-06-10 to 2026-06-15. Next period estimate 2026-06-29 from 28-day cycle and 14-day luteal phase.
Answer
2026-06-15
Live support
Estimated fertile window 2026-06-10 to 2026-06-15. Next period estimate 2026-06-29 from 28-day cycle and 14-day luteal phase.
Assumptions used
What this answer assumes
Estimate only; do not use as contraception or medical advice.
Cycle tracking is an estimate and does not guarantee pregnancy or contraception outcomes.
Irregular cycles, postpartum, medication, health conditions and age can change timing.
Use clinical advice for fertility treatment or contraception decisions.
Master’s Tip
How to use the result well
Master’s Tip: record real cycle dates over several months before trusting a single calculated window.
Printable record
What belongs in the saved calculation
Save the inputs, result, formula, assumptions, page URL and date together so the calculation can be reviewed later.
LMP year
2,026
LMP month
6
LMP day
1
Cycle length
28 days
Embeddable calculator
Embed this calculator
Copy a clean iframe version with the required CalculationTime attribution link built in.
Explain it like I'm 12
The ovulation calculator estimates the next period from cycle length, then subtracts luteal phase length to estimate ovulation and a fertile-window range.
Next period = LMP + cycle length. Estimated ovulation = next period − luteal phase. Fertile window = ovulation − 5 days through ovulation day.
Worked example
For LMP 2026-06-01, 28-day cycle and 14-day luteal phase, estimated ovulation is 2026-06-15 and the fertile window starts around 2026-06-10.
Professional note
Master’s Tip: record real cycle dates over several months before trusting a single calculated window.
Regional and unit assumptions
General menstrual-cycle estimate. Not contraception or medical advice.
Assumptions and limitations
Cycle tracking is an estimate and does not guarantee pregnancy or contraception outcomes.
Irregular cycles, postpartum, medication, health conditions and age can change timing.
Use clinical advice for fertility treatment or contraception decisions.
Methodology & Accuracy
How this calculator is checked
CalculationTime pages are built around visible arithmetic: the formula, assumptions, worked example and practical limitations are shown so the result can be checked rather than simply trusted.
Formula used
Next period = LMP + cycle length. Estimated ovulation = next period − luteal phase. Fertile window = ovulation − 5 days through ovulation day.
Standard or basis
General menstrual-cycle estimate. Not contraception or medical advice.
Where a calculator follows a named legal, trade or industry standard, that standard is cited visibly. Otherwise the page uses transparent general arithmetic and states its limits.
Master's Tip
Master’s Tip: record real cycle dates over several months before trusting a single calculated window.
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