Ember — BBT Tracker
Log your morning temperature, watch your coverline appear, and catch the thermal shift that confirms ovulation.
Ember is Babysential's free basal body temperature tracker. Log your waking temperature each morning — in Celsius or Fahrenheit — and the tool plots your curve, draws a coverline above your pre-ovulation baseline, and flags the sustained rise that confirms ovulation has happened. Your readings stay on your device when you're signed out, and sync to your account when you sign in.
According to ACOG, the post-ovulatory progesterone rise warms your resting temperature by a few tenths of a degree — the signal at the heart of every BBT chart. Because that rise is retrospective, BBT confirms ovulation rather than predicting it.
Trying to conceive? Pair Ember with our OPK tracker to anticipate ovulation from the LH surge, use the ovulation calculator to predict your fertile days, then switch to the due date calculator once you get a positive test.
Reading your BBT chart
Before ovulation, estrogen keeps your basal temperature in a lower range. After the egg is released, progesterone pushes it up and holds it there until your next period. The jump from the low range to the high range is the thermal shift. Ember sets your coverline at 0.05°C above the highest of your six pre-shift lows and confirms the shift once three consecutive readings sit above that line — the standard sympto-thermal rule described by ACOG.
Tips for accurate charting
- Same time, every morning: Measure before you sit up, talk, eat, or drink, after at least 3–4 hours of sleep.
- Use a basal thermometer: It reads to two decimal places, which matters because the shift can be just a couple of tenths of a degree.
- Note your outliers: Poor sleep, alcohol, illness, and travel can spike a reading — log a note so you can interpret it later.
- Combine signals: Pair BBT with an OPK and cervical-mucus changes for the clearest picture of your fertile window.
Frequently Asked Questions
What is basal body temperature (BBT) and why chart it?▾
Basal body temperature is your body's lowest resting temperature, measured first thing in the morning before you get up or move around. After ovulation, the hormone progesterone causes a small but sustained rise of roughly 0.2–0.5°C (0.4–1.0°F). Charting your daily BBT lets you see that shift and confirm that ovulation has occurred — useful both for trying to conceive and for understanding your cycle.
What is a coverline and how is it calculated?▾
A coverline is a horizontal line drawn just above your cluster of low pre-ovulation temperatures. The common rule is to take the highest of the six low days before the rise and add about 0.05°C (0.1°F). Once three days in a row sit above the coverline, you have a confirmed thermal shift. Ember draws your coverline automatically and marks the shift for you.
When does the temperature rise show ovulation?▾
BBT confirms ovulation after it happens, not before. The temperature rise appears one to two days after ovulation and is sustained through the rest of your cycle. The estimated ovulation day is usually the day before the first temperature above your coverline. Because the rise is retrospective, BBT is best paired with an ovulation predictor kit (OPK), which detects the LH surge before you ovulate.
How do I take an accurate basal body temperature?▾
Use a basal thermometer (it reads to two decimal places) and take your temperature at the same time each morning, after at least three to four hours of sleep, before getting out of bed, eating, drinking, or talking. Disrupted sleep, alcohol, illness, and travel can all nudge a reading up — note those days so you can interpret outliers. Consistency matters more than perfection.
Can BBT charting be used for birth control?▾
Fertility-awareness methods that include BBT can be used to avoid pregnancy, but only when learned thoroughly and applied carefully — effectiveness depends heavily on correct, consistent use. ACOG notes that fertility-awareness-based methods require training and discipline. If you are relying on cycle tracking for contraception, talk to your healthcare provider about which method fits you.