FERTILELog your periods, temperature, cervical mucus, ovulation tests and symptoms, see your fertile window and ovulation estimate on a calendar, chart your temperatures, compare cycles and work out a due date. Everything stays in your browser: nothing is uploaded.
Today's fertility
Log the first day of your last period under Log to see today's status, your fertile window and your next period.
Each day shows its estimated chance of conception. Colours follow the calendar legend.
Click a day on the calendar to see its status and everything logged for it.
| Started | Ended | Days | Cycle | Flow | Actions |
|---|
"Cycle" is the number of days from this period's first day to the next one's. Edit opens the entry in the form; Delete asks first.
Take it at the same time every morning, before getting up, talking or drinking, with a thermometer that shows two decimals. The chart is under Insights.
A positive test means the LH surge has started; ovulation usually follows within 24 to 36 hours. The tool uses the first positive of a cycle as that cycle's surge day.
| Cycle | Started | Length | Period | Ovulation | How known | Luteal | Logged |
|---|
"How known": a confirmed temperature shift, a positive ovulation test, or the calendar estimate. Luteal is the number of days from ovulation to the next period, which the tool can only count for finished cycles.
Estimated due date
--
Naegele's rule: 280 days from the first day of the last period, adjusted by the difference between your cycle length and 28 days. Only about one baby in twenty arrives on the date; a scan early in pregnancy gives a better one.
Used until you have logged two periods; after that the tool uses the average of your own recent cycles.
Days from ovulation to the next period. Usually 12 to 14; the Cycle by Cycle table shows yours once a temperature shift or a positive test has confirmed an ovulation.
Readings keep the unit they were entered in and are converted for display, so switching back and forth loses nothing. The theme follows the site: the moon button at the top right switches it.
Reminders show on the dashboard and, if you allow it, as a browser notification when you open the tool on the day. A browser page cannot wake up on its own, so nothing fires while the tool is closed.
The four-digit PIN keeps the screens hidden from anyone who picks up the device. It is stored as a scrambled hash and cannot be recovered: if you forget it, the only way back in is Clear all data. It does not encrypt what is stored.
Make a read-only calendar link for your partner. It carries only the dates needed for what you tick, packed into the link itself; nothing is stored anywhere.
The link shows the cycle as it is now. Make a new one after logging the next period.
CSV is one row per day for a spreadsheet or a doctor; the backup file restores everything here or on another computer; Print report prints the Insights section.
FERTILE is for personal tracking and information. It is not a medical device, not a contraceptive and not medical advice; its dates are estimates that can be days off. Talk to a doctor about anything that worries you. See the site's disclaimer.
Open Log, enter the first day of your most recent period, the last day if it is over, and the flow. The dashboard fills in at once: your cycle day and phase, the estimated ovulation day, the fertile window and the date of your next period. Add earlier periods too if you remember them; every one improves the estimates.
Under Settings, enter your usual cycle length and luteal phase if you know them; 28 and 14 are the defaults. Once two or more periods are logged, the tool switches to the average of your own recent cycles and says so on the dashboard. Pick the temperature unit and the first day of the week there as well.
Each morning, log your basal body temperature before getting up. Through the day, note the cervical mucus, the result of an ovulation test and any symptoms. A positive test or a confirmed temperature shift replaces the calendar estimate of ovulation for that cycle, so the fertile window and the next period follow what your body did.
The Calendar tab colours period days red, the fertile window in shades of green, the ovulation day in the brightest green and predicted days with a dashed edge. A dot marks days with symptoms. Click any day to see its status and everything logged for it, and to log something for that date.
Insights shows your average cycle, variation, period length and regularity, the temperature chart for any cycle with the coverline and the detected shift, a bar chart of cycle lengths, a cycle-by-cycle table with how each ovulation was known, and the due date calculator. Print report prints this section for a doctor's visit.
Settings holds reminders, a PIN lock for the screens, a read-only calendar link for your partner, export as CSV or as a backup file, import and Clear all data. The tool keeps everything in this browser only, so the backup file is the one copy that exists outside it.
Period dates, temperatures, test results and symptoms are among the most private things a person records. FERTILE has no account, no server and no sync. Everything lives in your browser's storage on your own device, and the only copy that leaves it is a file you export yourself or a link you choose to send.
A fixed 28-day calendar is wrong for most people. Once two periods are logged the tool averages your recent cycle lengths, and once a cycle has a positive ovulation test or a temperature shift it uses that instead of arithmetic. The dashboard always says which it is using.
Readings are charted by cycle day, not by calendar month, with a coverline drawn by the three-over-six rule that fertility awareness methods teach. The shift day is marked and the luteal phase it implies is counted, so you can see whether ovulation really happened and when.
Period, fertile window, ovulation, predictions, symptoms, temperature, mucus and test results all land on the same month view. One click on a day shows what was logged and lets you add to it, which is faster than paging through five separate logs.
Tick what to share, make a link, send it. The link itself carries the few dates needed, so nothing is stored anywhere and nothing can leak. The other person sees a read-only calendar with the upcoming days and nothing else.
Fertility prediction is an estimate, not a measurement. The tool labels every date as estimated or confirmed, shows the chance of conception as the average it is, and says plainly that it is not a contraceptive and not a substitute for a doctor.
Day 1 is the first day of bleeding, which usually lasts three to seven days. Through the follicular phase a follicle in the ovary ripens an egg while oestrogen rises, thickens the lining of the womb and turns cervical mucus from dry or sticky to creamy, watery and finally clear and stretchy. This phase is the variable one: it can be short or long, which is why cycle length varies.
A surge of luteinising hormone (LH) releases the egg about 24 to 36 hours after the surge begins, which is what an ovulation test detects. The egg lives 12 to 24 hours. Sperm can survive up to five days in fertile mucus, so the fertile window is the five days before ovulation and the day itself, with the two days before ovulation the most likely for conception.
After ovulation the empty follicle makes progesterone, which raises the basal body temperature by about 0.2 to 0.5 ยฐF (0.1 to 0.3 ยฐC) and holds it up until the next period. The luteal phase is fairly constant for each person, usually 12 to 14 days, which is why the tool counts back from the next period rather than forward from the last one.
Sperm can live up to five days in fertile cervical mucus. The egg survives 12 to 24 hours. A positive ovulation test comes before ovulation, a temperature rise after it. Stress, travel, illness, breastfeeding and big changes in weight or exercise can move ovulation by days or weeks. A cycle of 21 to 35 days is within the usual range.
"Everyone ovulates on day 14": ovulation day varies widely between people and between cycles. "You cannot get pregnant during your period": unlikely but possible with short cycles, since sperm can wait five days. "A regular cycle means ovulation every time": cycles without ovulation happen and can still bleed on time. "An app can replace contraception": it cannot.
Cycles consistently shorter than 21 days or longer than 35, or that become irregular after being regular. Trying to conceive for twelve months without success, or six months if over 35. Very heavy bleeding, bleeding between periods or severe pain. No period for three months when not pregnant. A tracker can show the pattern; only a doctor can say what it means.
Calendar estimate. The tool takes the first day of your last period and your cycle length, and places ovulation at cycle length minus luteal phase days later: day 14 of a 28-day cycle with a 14-day luteal phase, day 16 of a 30-day cycle. The fertile window is five days before ovulation to one day after. The next period is expected one cycle length after the last one started. With one period logged, the cycle length is the setting; with two or more, it is the rounded average of your last six cycles, ignoring any cycle shorter than 15 or longer than 60 days as a likely missed entry.
Confirmed ovulation. For the current cycle, a confirmed temperature shift places ovulation on the day before the first high temperature, and otherwise the first positive ovulation test places it on the day after the test. Either one replaces the calendar estimate for that cycle, and the dashboard says "confirmed by temperature" or "from your ovulation test" instead of "estimated". For finished cycles the same rules fill the Cycle by Cycle table and count the luteal phase.
The three-over-six rule. Looking at each cycle's temperatures by day, the tool finds the first day whose reading, and the two after it, are all above the highest of the six readings before it by at least 0.2 ยฐF (0.1 ยฐC). The coverline is drawn 0.1 ยฐF above that highest reading and the three days are marked. Readings with a note are shown but can be judged with that in mind; a fever or a short night can push one reading up without ovulation.
The chance of conception. The percentage on the dashboard and the week view is the day-specific chance of conception from intercourse on that day as measured by Wilcox, Weinberg and Baird in 221 women trying to conceive (New England Journal of Medicine, 1995): roughly 10% five days before ovulation, 16% and 14% on the next two, 27% and 31% on the two days before, 33% on the day itself. The study found no pregnancies after ovulation; the tool shows 5% the day after only to allow for error in the ovulation estimate. These are averages across many couples of many ages; your own odds depend on age, health and much else that a tracker cannot see.
Statistics. Average cycle and variation come from the gaps between the first days of your logged periods; average period from their lengths; regularity is 100 minus ten times the average difference of your cycles from their mean, so cycles within a day of each other score above 90. Two periods are the minimum, six or more give a fair picture.
Limits. Every date here is an estimate until a sign confirms it, and even a confirmed ovulation says nothing about the next cycle. Irregular cycles, recent hormonal contraception, breastfeeding, perimenopause and conditions such as PCOS make calendar estimates unreliable. FERTILE is not a contraceptive, not a diagnostic tool and not a substitute for a doctor.
From the first day of your last period, your cycle length and your luteal phase. Ovulation is estimated at cycle length minus luteal phase days after the period started (day 14 of a 28-day cycle with a 14-day luteal phase), and the fertile window runs from five days before that day to one day after, because sperm can live up to five days and the egg about one. Once you have logged two or more periods, the cycle length used is the average of your own recent cycles. A positive ovulation test or a confirmed temperature shift in the current cycle replaces the estimate for that cycle.
An estimated chance of conception from intercourse on that day, taken from a study that measured day-specific chances in 221 women trying to conceive (Wilcox, Weinberg and Baird, New England Journal of Medicine, 1995): about 10% five days before ovulation, rising to about 33% on the day itself, and close to zero outside the window. It is an average, not your personal odds, and it says nothing about any one cycle.
No. FERTILE is a tracking and information tool, not a contraceptive, and its predictions are estimates that can be days off, especially with irregular cycles. If you want to use fertility awareness to avoid pregnancy, learn a recognised method from a trained instructor or a doctor.
By the three-over-six rule used in fertility awareness methods: when three temperatures in a row are higher than the highest of the six before them, by at least 0.2 degrees Fahrenheit (0.1 degrees Celsius), the tool draws a coverline and marks the shift. Ovulation most likely happened the day before the first high temperature. Take the temperature at the same time every morning before getting up, and note poor sleep, illness or alcohol, which raise it.
Everything you log is kept in your browser's storage on this device under the tool's own name. Nothing is sent to a server and there is no account. The optional PIN keeps the tool's screens hidden until it is entered and is stored only as a scrambled hash, but it does not encrypt the stored data: anyone with full access to this browser profile could still read it. Export writes a backup file; Clear all data deletes everything, PIN included.
It is free, with no registration and no limits. Like every page on ZeroDataUpload, it is supported by advertising.