Ovulation calculator
Your fertile window, estimated in your browser
The six days when conception is possible, your estimated ovulation day, how many days past ovulation you are, and how long your luteal phase runs. An estimate for understanding your cycle or trying to conceive — not contraception.
Runs in your browser. Nothing you enter is sent anywhere — open your browser's network tab and check.
Start to start. 15–90.
Leave at 14 unless you know yours. 10–16.
How it is calculated
Anchored to the luteal phase, not to day 14
Most of the variation in a cycle happens before ovulation. The luteal phase — the days after ovulation, up to the day before the next period — is the steadier half. Steadier is not fixed: across 612,613 cycles Bull et al. measured a mean of 12.4 ± 2.4 days, which is the paper that exists to retire the 14-day assumption. So instead of assuming ovulation on day 14 of every cycle, the tool takes your cycle length, subtracts the luteal phase you give it, and places ovulation there: on the 14-day default, day 14 of a 28-day cycle, day 21 of a 35-day cycle, day 26 of a 40-day cycle. This is exactly how the PinkyBloom app places it — and it is only as good as the luteal number you feed it.
The fertile window is the five days before ovulation plus ovulation day — the six-day interval ending on the day of ovulation, which is how ASRM defines it, matching how long sperm survive and how briefly the egg does. (ACOG's patient FAQ runs a day longer, to one day after ovulation; we use ASRM's six.) The window is an estimate of where those six days most likely fall; only an ovulation test or a temperature shift shows where they actually fell.
DPO counts from ovulation day as 0. Luteal length counts the days after ovulation up to the day before bleeding — the one definition used everywhere on this page — so a 28-day cycle with ovulation on day 14 has a 14-day luteal phase, and the next period arrives at 15 DPO rather than 14. That is the same convention the estimate uses, so the two tools agree with each other.
Questions
Asked in your words
The same math, on your phone
Every cycle, learned from your own dates
PinkyBloom runs this estimate on your phone, from the periods you actually log — so the cycle length is yours, not a default. If you pair with your partner, PinkyBond gives him the forecast in plain words, never your log.
Free on iPhone and Android. No account, no email, no phone number. Your health data stays on your phone unless you turn on iCloud backup or partner sharing — and we can't read it either way.
