Example 1
- LMP: January 1, 2026
- Cycle length: 28 days
Ovulation: Jan 14
Window: Jan 9-15
A typical 28-day cycle: ovulation lands roughly midway, matching the textbook model.
Ovulation calculator
Type the first day of your last period and cycle length. From January 1, 2026 and 28 days: ovulation January 14, window 9-15. At 32 days it is January 18. A model, not an LH test.
Ovulation ≈ LMP + (cycle − 14). Window: 5 days before plus that day. Not contraception. Pregnancy gain lives on pregnancy weight gain. Due date sits in the date hub.
Result
Enter the first day of your last period.
How results are calculated
Ovulation: LMP + (cycle length − 14 days).
Fertile window: from 5 days before ovulation through the day of ovulation (a 6-day range).
Next period: LMP + cycle length.
January 1, 2026 and a 28-day cycle: ovulation January 14, window 9-15, next period January 29. At 32 days ovulation moves to January 18, window 13-19. At 24 days: January 10, window 5-11. The luteal phase is a fixed 14 days here; the difference sits in the phase before ovulation.
Type the bleed-start date. Cycle length can stay 28, or you type a 21-45 average. Click Calculate. A blank cycle field fills 28, as the hint under the field says.
A calendar, not contraception and not a fertility workup. Stress, illness, or a routine change can move the day by a few. Pregnancy weight gain and due date are separate cards once planning turns into pregnancy. An LH test does not move the ovulation date.
How to use
- Type the first day of your last period, for example January 1, 2026.
- Type average cycle length, for example 28. If you do not know, leave 28; a blank cycle field also uses 28.
- Click Calculate. On 28 days from January 1, ovulation lands on January 14, window 9-15.
- At 32 days the same start date gives January 18 and window 13-19. At 24 days: January 10.
- A fertile window from cycle length. Once you are pregnant, gain lives on the pregnancy-gain card, not here.
LMP, ovulation, and the luteal offset
Start at the first day of the last period, then add cycle length minus 14. From January 1, 2026 and 28 days, ovulation is January 14, window 9-15.
- LMP
- Last menstrual period, the first day of bleeding. With LMP January 1, 2026 and a 28-day cycle the formula places ovulation on January 14.
- ovulation
- The estimated day LMP + (cycle − 14). At 32 days from the same start that is January 18, not 14, because the luteal span stays 14 days.
- LH
- Luteinizing hormone from a strip test. This calculator does not read it: January 14 on a 28-day cycle is a calendar model, not an LH peak.
Usage examples
Example 2
- LMP: January 1, 2026
- Cycle length: 32 days
Ovulation: Jan 18
Window: Jan 13-19
A longer cycle shifts ovulation later - the luteal phase stays fixed, so the difference comes from the pre-ovulation phase.
Example 3
- LMP: January 1, 2026
- Cycle length: 24 days
Ovulation: Jan 10
Window: Jan 5-11
A shorter cycle means earlier ovulation - worth factoring into planning.
Example 4
- LMP: 2026-03-02
- Cycle: 28
Ovulation: Mar 16
Window: Mar 11-16
When is ovulation after 2026-03-02 with a 28-day cycle? Ovulation: Mar 16, Window: Mar 11-16.
Example 5
- LMP: 2026-06-12
- Cycle: 30
Ovulation: Jun 28
Window: Jun 23-28
When is ovulation after 2026-06-12 with a 30-day cycle? Ovulation: Jun 28, Window: Jun 23-28.
Example 6
- LMP: 2026-09-20
- Cycle: 32
Ovulation: Oct 8
Window: Oct 3-8
When is ovulation after 2026-09-20 with a 32-day cycle? Ovulation: Oct 8, Window: Oct 3-8.
Example 7
- LMP: 2026-11-05
- Cycle: 35
Ovulation: Nov 26
Window: Nov 21-26
When is ovulation after 2026-11-05 with a 35-day cycle? Ovulation: Nov 26, Window: Nov 21-26.
Example 8
- LMP: 2026-01-18
- Cycle: 21
Ovulation: Jan 25
Window: Jan 20-25
When is ovulation after 2026-01-18 with a 21-day cycle? Ovulation: Jan 25, Window: Jan 20-25.
Related calculators
FAQ
When is ovulation after January 1, 2026 on a 28-day cycle?
Day 14, January 14. Window January 9-15. Next period January 29. A model with a 14-day luteal phase.
What about a 32-day cycle from the same date?
Ovulation January 18, window 13-19. A longer cycle moves the day later, because you subtract 14 from 32, not from 28.
On a 35-day cycle is ovulation still day 14?
No. 35 − 14 = 21. Typing a 28-day template on a long cycle places the window too early.
Why is the window 6 days?
Sperm can live several days; the egg about a day. So 5 days before plus ovulation day.
Can I use this as contraception?
No. The calendar is too rough. For contraception you need a proven method with a doctor or pharmacist.
What if my cycles are irregular?
The calendar gets less reliable. Track a few cycles, mucus, or LH tests, or talk with your doctor.
Can I get pregnant outside this window?
Yes, especially if ovulation shifts. The window is highest chance in this model, not a promise of safe days.
What about a 24-day cycle from January 1, 2026?
Ovulation January 10, window 5-11. A shorter cycle pulls the day earlier.
When should I enter the period date?
Best on the day bleeding starts, while you still remember it. Guessing the date throws off the whole estimate.
What should I open once planning becomes pregnancy?
Weight gain from pre-pregnancy BMI, and due date. Adult BMI bands do not judge pregnancy gain.
Knowledge sources
Ovulation from LMP and cycle length. This is not contraception.
Page updated in 2026.