Basal Body Temperature Chart
Build a dated BBT record from your own temperature readings. View the chart, keep measurement notes and download a backup to continue your log on a later visit.
A record, not an ovulation diagnosis. This tool does not confirm pregnancy, identify an exact ovulation day or label any day safe for unprotected sex.
Start your chart →Add a Reading to Your Cycle Log
Set cycle day 1, then record one temperature per date. Your chart shows added entries only; typing into the form does not change the log.
Your recorded chart will appear here
Add your first dated reading or try fictional data below. Celsius and Fahrenheit show the same recorded temperatures in different units.
Keep the measurement context
Time and notes stay beside each date. The tool does not correct a reading for sleep, illness or measurement method.
Missing days remain missing
Unrecorded days are not filled with averages or joined into an invented continuous line.
A chart is not contraception
No safe-day labels, ovulation markers, pregnancy badges or hormone diagnoses are calculated.
Your recorded BBT chart
Fictional example data. This is not a real cycle or a diagnostic pattern. Clear the sample log before recording your own readings.
Vertical scale adapts to recorded values. Only consecutive recorded dates are connected. No coverline or fertile-day shading is calculated.
Downloaded files contain cycle dates and may contain personal notes. Keep them private. Only the JSON backup can be restored in this tool.
View or edit recorded rows ↓Reads a backup from this tool locally. No file upload. Maximum 128 KiB; replacement requires confirmation when a log is already open.
Replace the current log? Download a JSON backup first if you want to keep it. You can undo one log change during this session.
Medical disclaimer: This is a temperature-recording and charting aid, not a diagnostic test or a contraceptive method. It does not confirm ovulation, pregnancy, anovulation, PCOS or a luteal-phase problem. Do not use it to decide when unprotected sex is safe or change treatment. Ask a qualified clinician about persistent cycle concerns, and use an appropriate pregnancy test if pregnancy is possible.
Dated readings and measurement notes
These are the entries in the chart, not the unfinished form above. Edit a date to update its temperature or note. Remove changes the log immediately; Undo restores one prior log change.
| Date | Cycle day | Temperature | Time | Note | Actions |
|---|
Build a dated record without filling in missing days
Three fictional logs demonstrate a changing pattern, gaps and a flat series.
| Step | What to do | What this chart does |
|---|---|---|
| 1 · Set the cycle date | Choose the first day of your period as day 1. | Counts calendar days from the chosen date; it does not assume ovulation on day 14. |
| 2 · Record a measurement | Use a consistent thermometer and measurement method, following its instructions. | Stores the entered reading, optional local time and note. |
| 3 · Keep gaps honest | Leave days without a measurement unrecorded. | Plots dated points; a missing date breaks the connecting line. |
| 4 · Save and continue | Download JSON before leaving; restore it on a later visit. | CSV is for reviewing rows; SVG is a chart image. They do not restore a session. |
A visible rise, without a diagnosis
Ten readings dated 1–10 January 2025. Higher values appear later in the sample; the chart does not label an ovulation day or confirm that ovulation happened.
Five readings across nine days
Readings on sample cycle days 1, 2, 5, 6 and 9. Missing days remain gaps. Notes and exact values stay available in the table.
Four equal readings
Four fictional readings at 36.50 °C, shown as 97.70 °F. A flat sample is a plotting example, not evidence of a hormone problem or an anovulatory cycle.
What the temperature line can and cannot tell you
Keep an observation separate from an ovulation, pregnancy or hormone diagnosis.
A temperature rise is not an exact ovulation timestamp
BBT may show a change after ovulation, but a chart alone cannot reliably establish its exact day. This tool applies no three-high-readings rule, coverline or automatic ovulation confirmation.
An unclear pattern is not a diagnosis
Some people who ovulate do not record a clearly biphasic chart. A flat or variable line alone does not diagnose anovulation, PCOS, low progesterone or a luteal-phase defect. Share concerns with a clinician rather than assigning a label from the graph.
Record conditions instead of inventing corrections
Take readings consistently on waking, before getting out of bed, using the same method. Note circumstances that might affect interpretation. The tool neither adds degrees for a late reading nor removes a point because its note mentions illness.
Use a thermometer according to its instructions
A digital oral or basal thermometer with appropriate precision may be used for BBT recording. Keep the measurement method consistent. Two displayed decimal places do not guarantee accuracy, and a unit conversion cannot add thermometer precision.
A saved file is your copy of the log
This page has no automatic localStorage or account history. A JSON backup retains the readings for restore; CSV contains reviewable rows in both units and SVG contains the chart. A saved download does not vanish when the page is closed.
This page cannot mark a day safe for sex
Fertility-awareness contraception involves learning a method and interpreting more than this chart. The tool does not provide a contraceptive protocol or protection from sexually transmitted infections. Ask a trained professional if you want to use fertility awareness.
Persistent high readings are not a pregnancy result
The chart does not display an “18 high days” pregnancy badge. If pregnancy is possible, use a pregnancy test according to its instructions. See the NHS testing guide rather than drawing a conclusion from temperature alone.
A short log is still an incomplete record
The day-span statistic is simply the first-to-last recorded day; it is not an estimated cycle length. No next period, fertile window or pregnancy chance is calculated. Additional notes and clinical history may matter more than the shape of one line.
Read ASRM’s evaluation guidance and BBT limitations, Mayo Clinic’s measurement overview, NHS fertility-awareness guidance and the NHS pregnancy-test guide.
Related cycle tools and health references
Calendar estimates answer different questions from a temperature log. Use the original health sources to check the interpretation limits.
Useful resources
Bhavin Sheth maintains this page. Health references explain charting limitations; they do not endorse this tool. No medical review, clinical validation, pregnancy-detection accuracy or contraceptive effectiveness is claimed for this implementation.
Questions about readings, backups and chart interpretation
Know which information is recorded and which conclusions the tool does not calculate.
Does this BBT chart confirm an ovulation date?
No. It plots the readings you enter and applies no ovulation-detection rule. A temperature pattern alone cannot reliably establish an exact ovulation date.
Can a flat chart diagnose a hormone or ovulation problem?
No. Missing data, measurement conditions and other factors can affect a chart. A flat or variable pattern alone does not diagnose anovulation, PCOS, low progesterone or a luteal-phase problem.
Can I use the chart to identify safe days for unprotected sex?
No. This tool does not provide a contraceptive method or safe-day labels. Seek qualified fertility-awareness or contraception advice rather than relying on this graph.
Will my entries be here when I return?
Not automatically. Entries stay only in this page’s memory and are lost on refresh or close. Download the JSON backup before leaving and restore it on the next visit. No account or browser-storage history is created.
Which downloaded file can I restore?
Only the JSON backup created by this tool. CSV is for reviewing rows in a spreadsheet and SVG is the chart image. A restore is processed locally and validated before it can replace the current log.
What happens if I record the same date twice?
The later submission updates that date instead of adding a duplicate. If you change the date while editing, the submission adds or updates the newly selected date; it does not move the old entry.
How are missing dates and cycle days handled?
Day 1 is the cycle-start date you choose. Each later calendar date increments the day number. Missing dates are not estimated, and lines connect consecutive recorded dates only.
Does changing Celsius or Fahrenheit change the readings?
No. The log keeps canonical Celsius values and converts the display using °F = °C × 9/5 + 32. Changing the unit also converts an entered draft; conversion does not improve measurement precision.
Can high temperatures tell me that I am pregnant?
Not reliably. This tool does not diagnose pregnancy or assign a pregnancy probability. Use a pregnancy test according to its instructions if pregnancy is possible.
Are my notes uploaded or stored by this script?
No. The script reads and charts entries in page memory, including locally restored backup files. Downloads create files on your device. Fonts and other website scripts may make separate requests; this statement applies to this charting script only.