FERTILE Help Documentation

A complete guide to the ovulation and fertility tracker, from the first logged period to the backup file.

Last Updated: October 7, 2026

1. Getting Started

1.1 What you need

• A modern browser (Chrome, Edge, Firefox, Safari or Opera) with JavaScript enabled, on a computer, tablet or phone
• Site data allowed for zerodataupload.com, so your entries are kept between visits
• The first day of your last period; everything else is optional

1.2 The layout

The tool is one page. The toolbar shows a status pill with today's cycle day and phase and today's date on the left, and five pill tabs on the right: Dashboard, Calendar, Log, Insights and Settings. On a phone the tabs fill one row and the date is hidden. Show the welcome in Settings opens a short summary with a button that takes you straight to the period log.

2. The Dashboard

• Cycle ring: today's cycle day over your expected cycle length, as a ring that fills through the cycle.
• Today's fertility: Period, Low, Medium, High or Peak fertility, or Period expected when the period is late; the estimated chance of conception for today; a sentence saying when ovulation is or was and how it is known; chips with the days to ovulation, the days to the next period and the cycle length in use.
• This Week: the seven days of the current week (starting on the day you chose under Settings) coloured as on the calendar, each with its chance.
• Coming Up: today's reminders, then the next events in date order: the fertile window opening, ovulation, the next period, and the next cycle's window and ovulation when the current ones have passed.
• Logged Recently: your last period, temperature, mucus entry, test and symptom day.
• Quick Log: buttons that open the matching log form, plus one for Insights.

3. The Calendar

The Calendar tab shows one month with the arrows and the Today button at the top right. Each day is coloured by its status: red for a period day (paler for a light flow), three greens for the fertile window from low to high chance, deep green for the ovulation day, and a dashed edge for a predicted day in the future. One, two or three dots under the number mean that symptoms, a temperature, or a mucus or test entry were logged. Click a day to open it in the card beside the calendar: its status, chance and cycle day, the period note, the temperature with its time and note, the mucus type, the test result and the symptoms, with buttons that open the log forms for that date. On a phone the card sits under the calendar and the page scrolls to it. The left and right arrow keys change the month.

4. Logging Periods

Log, Period. Enter the first day, the last day if the period is over (add it later otherwise), the flow and an optional note, then Save period. The table beside the form lists every logged period with its length in days, the length of the cycle it started (the days to the next period, or "current, day N"), the flow, and Edit and Delete buttons. Edit loads the entry into the form; Delete asks first and leaves the temperatures, tests and symptoms of those days in place.

The form refuses a first day in the future, a last day before the first, a period longer than 15 days and a period starting within ten days of one already logged, which stops accidental double entries. A period without a last day is shown on the calendar with your average period length (five days until you have logged some).

5. Logging Temperature, Mucus, Tests and Symptoms

5.1 Temperature

Log, Temperature. Enter the date, the reading in the unit chosen under Settings (93.00 to 102.50 °F or 34.00 to 39.00 °C), the time it was taken and a note when something could have raised it: a short night, illness, alcohol, a much later time. One reading per day; saving again replaces it. The list beside the form shows the last seven readings with a delete button. Take the reading first thing in the morning, before getting up, at about the same time every day, after at least three hours of sleep, with a thermometer that shows two decimals.

5.2 Cervical mucus

Log, Mucus. Pick the date and one of five types, each with its fertility meaning and a short description: dry and sticky (low), creamy (medium), watery (high) and egg white (peak). Save entry. The entry shows on the calendar and in the day card; it does not move the ovulation estimate.

5.3 Ovulation (LH) tests

Log, LH test. Pick the date and time, the result (negative, almost, positive) and the strength of the test line from 1 to 10 against the control line. The first positive of a cycle becomes that cycle's surge day and places ovulation on the day after it (see section 6).

5.4 Symptoms

Log, Symptoms. Pick the date, tap any of the twelve symptoms (cramps, bloating, breast tenderness, headache, fatigue, mood swings, acne, ovulation pain, backache, nausea, high libido, insomnia), add a note, Save symptoms. Changing the date loads what was saved for that day so you can add to it; Remove this day's symptoms deletes the entry.

6. How Ovulation and the Fertile Window Are Placed

• Cycle length: the setting until two periods are logged, then the rounded average of your last six cycles, ignoring cycles shorter than 15 or longer than 60 days.
• Calendar estimate: ovulation at cycle length minus luteal phase days after the last period started; for finished cycles, luteal phase days before the next period. The fertile window is five days before ovulation to one day after. The next period is one cycle length after the last one started.
• Temperature shift: when three readings in a row are at least 0.2 °F (0.1 °C) above the highest of the six readings before them, the first of the three is the shift day and ovulation is placed on the day before it. The coverline is drawn 0.1 °F above that highest reading.
• Positive test: without a shift, the first positive test of the cycle places ovulation on the following day.
• Precedence: temperature shift, then test, then estimate. The dashboard, the day card and the Cycle by Cycle table say which applies.
• Chance of conception: 10% five days before ovulation, 16%, 14%, 27% and 31% on the following days, 33% on the day, 5% the day after, 0% otherwise; averages from Wilcox, Weinberg and Baird (New England Journal of Medicine, 1995), not personal odds; the 5% the day after only allows for error in the ovulation estimate.

7. Insights: Statistics and Charts

• Four tiles: average cycle (with the number of cycles behind it), variation (shortest to longest), average period (bleeding days of periods with an end date) and regularity (100 minus ten times the average difference from the mean, with a word for it). They need two periods.
• Temperature Chart: readings by cycle day for the cycle picked in the list at the top right, the coverline when a shift was found, the three shift days as larger green points, noted readings in orange, and a sentence under the chart with the shift day, the coverline and the ovulation date, or why no shift was found. Hover a point for the date, reading and note.
• Cycle Lengths: a bar per finished cycle (the last twelve), orange outside 21 to 35 days, and under it notes on your average and range, your luteal phase from confirmed ovulations, cycles outside the usual range and how often ovulation pain fell near the estimate.
• Cycle by Cycle: the last twelve cycles with first day, length, period length, ovulation date, how it is known, luteal phase and what was logged. The current cycle is highlighted.

8. The Due Date Calculator

Insights, Due Date Calculator. It fills in from your last logged period and your cycle length; change either freely. Calculate shows the estimated due date (280 days from the first day of the last period, adjusted by the difference between the cycle length and 28), the likely conception date, how many weeks and days along you would be today, the trimester and the progress through 40 weeks. A date in the future or more than 45 weeks ago is refused.

9. Settings and Reminders

• Cycle: cycle length (20 to 45 days) and luteal phase (9 to 18, at least six days shorter than the cycle). The hint under the cycle length says whether the setting or your average is in use.
• Display: temperature unit and the first day of the week. Both apply at once; readings keep the unit they were entered in.
• Reminders: five switches: period approaching (two days before), fertile window starting (the day before), ovulation day, log your temperature (every morning until logged) and take an ovulation test (each day of the window until logged). Due reminders show at the top of Coming Up on the dashboard. Allow browser notifications shows them as a notification as well, once a day, when you open the tool; a page cannot notify you while it is closed.

10. The PIN Lock

Settings, PIN Lock. Switching it on opens a window for a four-digit PIN entered twice; 1234, 0000 and four equal digits are refused. From then on the tool opens on a lock screen and shows nothing until the PIN is entered (type the four digits, or paste them). Change PIN sets a new one; switching the lock off asks for confirmation. The PIN is stored only as a scrambled hash with a random salt, so it cannot be read back or recovered: the lock screen's only way out without it is Forgot it? Clear all data, which deletes everything. The lock hides the screens; it does not encrypt the stored data, and anyone with full access to the browser profile could still read it.

11. Partner Sharing

Settings, Partner Sharing. Tick what to share (fertile window, ovulation day, period dates), Make a share link, Copy. The link carries the first day of your last period, your cycle length and luteal phase, your average period length, the week start and, if period dates are ticked, the first and last days of your last six periods, packed into the part of the address after the # sign, which browsers do not send to the server. Whoever opens it sees a read-only month calendar with the chosen layers, the coming days and a button to open their own tracker; nothing they do touches your data or theirs. No temperatures, tests, mucus, symptoms or notes are ever in the link. It shows the cycle as it was when made, so make a new one after logging the next period.

12. Export, Import, Print and Clear

• Export CSV: one row per day with anything logged: date, cycle day, status, chance, period and flow, temperature with unit and time, mucus, test result and line strength, symptoms and notes. For a spreadsheet or a doctor.
• Export backup: one file with everything except the PIN. Import backup reads such a file (or an export from the earlier version of the tool), shows what it holds and, after confirmation, replaces what is in this browser. The PIN set here stays.
• Print report: switches to Insights and prints it on plain paper, without the rest of the page.
• Clear all data: after confirmation, deletes every period, temperature, test, symptom and setting the tool stored in this browser, the PIN included. Show the welcome opens the short summary of how the tool works.

13. Keyboard Shortcuts

• 1 to 5: switch to Dashboard, Calendar, Log, Insights or Settings (when no field has the focus)
• Left and right arrows: previous and next month on the Calendar tab
• Enter: on the lock screen, check the PIN (the fourth digit also does)
• Esc: close a window

14. What Is Remembered

One entry in the browser's storage under the tool's own name holds everything: the periods, the temperatures with their unit, the mucus entries, the test results, the symptoms with their notes, the cycle and display settings, the reminder switches, the PIN hash and salt, whether the welcome was seen and the day of the last notification. It is written after every change and every value is checked when it is read. If the earlier version of FERTILE left its data in this browser under its old names, it is read once on the first visit, checked, carried over (temperatures as Fahrenheit, the PIN re-stored as a hash) and the old copies removed. The theme is the site's own setting, shared with every page.

15. Troubleshooting

• The dashboard says No period logged: log the first day of your last period under Log. Everything else follows from that date.
• The dates look wrong: check the cycle length and luteal phase under Settings, and whether a period is missing from the table, which makes one long cycle out of two.
• No temperature shift is found: the rule needs nine readings, six low and three high, all three at least 0.2 °F (0.1 °C) above the six. Fill the gaps and use a two-decimal thermometer.
• A period will not save: see the rules in section 4; to correct an existing period, use Edit in the table.
• Notifications do not appear: allow them under Settings and in the browser; they come once a day, only when due and only while the tool is open.
• The data vanished: site data was cleared, or this is a private window or another browser or profile. Only a backup file brings it back.
• The PIN is lost: the only way in is Forgot it? Clear all data on the lock screen.