The ovulation calculator uses last period start and cycle length with a common “cycle minus 14 days” rule for ovulation, fertile window, and next period.
How to use
- Pick the first day of your last period.
- Enter average cycle days (21–45)—chips for 26/28/30/32.
- Read the timeline; LMP also feeds the due date calculator when planning pregnancy dates.
Example
LMP Oct 1, 28-day cycle → ovulation ~Oct 15, fertile window ~Oct 10–16 (rounded).
Not a substitute for ovulation tests or medical advice.
Frequently asked questions
How is ovulation estimated?
From the first day of your last period, subtract about 14 days from cycle length (typical luteal phase) to estimate ovulation, plus a fertile window and next period.
What cycle length should I use?
Use your average cycle length over recent months (about 21–45 days accepted here). Very irregular cycles make calendar methods unreliable—use ovulation tests or clinical guidance.
Which days are “fertile”?
About 5 days before estimated ovulation through 1 day after is shown as a fertile window—for awareness only, not sole contraception or conception planning.
Same as the due date calculator?
Different goals: due date estimates gestational age and delivery date; this page estimates ovulation and fertility timing. LMP can be the same input, different outputs.
Replace ovulation kits?
No—kits detect hormone surges; this is calendar math only. For conception or contraception, use approved testing and medical advice.
Time zones or travel?
Calculations use the calendar dates you enter—no time zones. After travel, use the local date you recorded for LMP.
Can I save period date and cycle?
Yes. Copy link below the form keeps your current inputs so you can share the scenario or save it for later.