BBT Charting: The Complete Guide to Basal Body Temperature Tracking

Basal body temperature charting seems intimidating at first - taking your temperature every single morning before you even sit up? But it's actually straightforward once you get the hang of it, and the information it provides about your fertility is invaluable. This guide covers everything you need to know to start charting effectively.

What Is Basal Body Temperature?

Your basal body temperature (BBT) is your body's lowest resting temperature, measured when you're completely at rest. After ovulation, the hormone progesterone causes your BBT to rise by about 0.4-1.0°F and stay elevated until your next period. By tracking this temperature shift, you can confirm ovulation occurred and identify your fertile window.

Why Track BBT?

BBT charting tells you things that ovulation predictor kits and apps can't:

• Confirms ovulation actually happened: OPKs only detect the LH surge, not actual egg release. BBT shows that ovulation occurred.
• Reveals your luteal phase length: Critical for diagnosing luteal phase defects
• Identifies pattern problems: Slow rise, weak rise, or erratic temps can indicate hormonal issues
• Predicts your period: Temperature drops 1-2 days before menstruation
• Early pregnancy sign: If your temperature stays elevated past 16-18 days post-ovulation, you're likely pregnant
• Free: Unlike OPKs or fertility monitors, charting only requires a $10-15 thermometer

What You Need to Start

A Basal Body Thermometer

Regular fever thermometers aren't precise enough. You need a basal thermometer that measures to two decimal places (98.12°F instead of just 98.1°F). Digital basal thermometers cost $10-20 and are available at any drugstore or online.

Some thermometers have memory to store your last reading, which is handy if you fall back asleep before recording it.

A Charting Method

You can track temps with:

• Paper charts: Free printable charts or fertility awareness books
• Apps: Fertility Friend, Kindara, or Ovia (apps can detect patterns automatically)
• Spreadsheet: Make your own in Excel or Google Sheets

Consistency

BBT charting requires taking your temperature at the same time every morning before you get out of bed or do anything else. Set an alarm, even on weekends.

How to Take Your BBT

The Basics

1. Same time every day: Take your temp at the same time each morning, ideally within 30 minutes. Your body temp naturally rises as the day progresses, so timing consistency is critical.
2. Immediately upon waking: Before sitting up, talking, drinking water, or using the bathroom. Keep your thermometer on your nightstand.
3. After at least 3-5 hours of sleep: You need uninterrupted rest for an accurate reading. If you get up in the night, temp yourself when you've had at least 3 consecutive hours of sleep.
4. Same location: Oral (under tongue), vaginal, or rectal. Oral is most common and easiest. Vaginal/rectal are slightly more accurate but not necessary for most women.
5. Keep thermometer in place: For digital thermometers, wait for the beep. For mercury thermometers (rare now), wait 5 minutes.

Recording Your Temperature

Immediately write down or enter your temperature. Record it to two decimal places (like 97.34°F or 36.32°C). If using an app, it will plot the point on a graph automatically.

Understanding Your BBT Chart

Normal BBT Pattern

A typical chart has two distinct phases:

Follicular Phase (Before Ovulation)

• Lower temperatures (usually 97.0-97.7°F or 36.1-36.5°C)
• Relatively flat or slightly variable
• Lasts from period until ovulation (varies by woman)

Luteal Phase (After Ovulation)

• Higher temperatures (usually 97.8-98.8°F or 36.6-37.1°C)
• At least 0.4°F (0.2°C) higher than pre-ovulation temps
• Stays elevated for 12-16 days until your next period
• Drops 1-2 days before period starts

Identifying Ovulation

You can't predict ovulation with BBT - you can only confirm it after the fact. Here's how to spot it:

• Temperature shift: Look for a sustained rise of at least 0.4°F above your average pre-ovulation temps
• Three elevated temps: Most charting methods require three consecutive temps higher than the previous six days
• Ovulation day: Typically the last day before the temp rise, or occasionally the first day of the rise

Once you see three elevated temps in a row, you can be confident ovulation happened. By then, your fertile window has closed for that cycle.

What Different Chart Patterns Mean

Biphasic Pattern (Normal)

Two distinct temperature phases with a clear shift after ovulation. This is what you want to see - it confirms you ovulated.

Monophasic Pattern (Anovulatory)

Temperatures stay relatively flat throughout the cycle with no sustained rise. This indicates you didn't ovulate that cycle. Occasional anovulatory cycles are normal, but if it happens frequently, see your doctor.

Slow Rise Pattern

Temperature increases gradually over 3-5 days instead of spiking quickly. This can still indicate ovulation, though it makes pinpointing the exact day trickier. Some women consistently have slow rise patterns and it's normal for them.

Triphasic Pattern (Possible Pregnancy)

After the initial post-ovulation rise, temps climb even higher around 7-10 DPO and stay elevated. This third phase is associated with pregnancy, though not all pregnant women see it and not all triphasic charts result in pregnancy.

Erratic Temps (Disturbed Sleep/Illness)

Wild temperature swings from day to day usually mean something disrupted your sleep or you're getting sick. Note any factors (alcohol, poor sleep, stress, illness) so you can discard outlier temps.

Factors That Affect BBT

Many things can cause temperature fluctuations that have nothing to do with ovulation:

• Sleep disruption: Less than 3 hours of consecutive sleep, waking up much earlier/later than usual
• Alcohol: Even one drink can raise your temp the next morning
• Illness/fever: Being sick elevates your baseline temperature
• Stress: High stress can affect temps
• Travel and time zone changes: Throws off your sleep pattern
• Electric blanket or very warm room: External heat sources raise BBT
• Medication: Some drugs affect body temperature

When any of these factors apply, note them on your chart. Charting apps let you mark "disturbed sleep" or other variables. You can often discard outlier temps that don't fit the overall pattern.

Using BBT with Other Fertility Signs

BBT works best when combined with other ovulation tracking methods:

Cervical Mucus

Check your cervical mucus daily and record it on your chart. Fertile mucus (clear, slippery, stretchy like egg whites) appears 2-3 days before ovulation. The last day of fertile mucus is usually ovulation day, which you'll confirm with your temp rise.

Ovulation Predictor Kits

OPKs predict ovulation 24-36 hours in advance (detecting LH surge), while BBT confirms it happened. Using both gives you advance warning to time intercourse and retrospective confirmation.

Cervical Position

Your cervix changes position and texture throughout your cycle. Around ovulation, it becomes soft, high, open, and wet (SHOW). After ovulation and BBT rise, it drops lower and becomes firm and closed.

When to Have Intercourse Based on BBT

Since BBT only confirms ovulation after it's already happened, you can't rely on it alone for timing. However, after charting 2-3 cycles, you'll see patterns:

• If you typically ovulate on day 14, start having sex every other day starting around day 10-12
• Watch for fertile cervical mucus as your signal to increase frequency
• Once you confirm ovulation with three elevated temps, you can stop trying for that cycle

The most fertile days are the 2-3 days before ovulation and the day of ovulation. Sperm can survive 3-5 days in fertile cervical mucus, so regular intercourse in the days leading up to ovulation is ideal.

How Long to Chart

Chart for at least 2-3 cycles before making conclusions about your patterns. This helps you learn:

• Your typical ovulation day
• Your luteal phase length
• Whether you're ovulating consistently
• If there are any concerning patterns

Continue charting as long as you're trying to conceive. Many women keep charting into early pregnancy to watch for the sustained temperature elevation that indicates pregnancy.

Detecting Early Pregnancy with BBT

If your luteal phase temperatures stay elevated for more than 16-18 days, pregnancy is very likely:

• 16 days elevated: Period should have started by now - take a test
• 18 days elevated: Very strong pregnancy sign - definitely test
• Triphasic pattern: Third temp rise around implantation (7-10 DPO) is a good sign but not definitive

Some women see a temporary dip in temperature around 7-10 DPO (implantation dip), then temps rise again. This is associated with pregnancy but not all pregnant women experience it.

Use our Pregnancy Test Calculator to determine the best day to test once your temps have been elevated for 14+ days.

Common BBT Charting Mistakes

Temping at Different Times

Taking your temp at 6am one day and 8am the next creates artificial fluctuations. Stick to the same time within 30 minutes.

Not Temping First Thing

Getting up to use the bathroom, checking your phone, or sitting up before temping will raise your temperature and give inaccurate readings.

Switching Thermometers Mid-Cycle

Different thermometers can give slightly different readings. Use the same one for the entire cycle.

Expecting Perfect Charts

Real charts have bumps and variations. You're looking for overall patterns, not perfectly smooth curves. Don't stress over individual outliers.

Giving Up Too Soon

The first cycle often feels confusing because you're learning the method and your body's patterns. Keep going - it gets easier.

When to See a Doctor About Your Charts

Bring your charts to your doctor if you notice:

• No sustained temperature rise for multiple cycles (anovulation)
• Luteal phase consistently 10 days or shorter (luteal phase defect)
• Very weak temperature rise (less than 0.4°F) after ovulation
• Slow rise pattern every cycle (may indicate low progesterone)
• You've been charting and trying for 6+ months without success (12+ months if under 35)

Your charts provide valuable diagnostic information that can help your doctor identify hormonal issues or other fertility problems.

BBT Charting Apps

Apps make charting much easier by automatically plotting your temps and detecting patterns:

Fertility Friend

The most sophisticated charting app. It uses an algorithm to detect ovulation based on your temps and other signs. Free version includes all essential features. Great for learning the fertility awareness method.

Kindara

Beautiful interface with good charting tools. Allows you to track temps, cervical mucus, OPKs, and more. Social features let you share charts with your partner.

Ovia Fertility

Combines BBT charting with general fertility tracking. Less detailed than Fertility Friend but easier for beginners.

The Bottom Line

Basal body temperature charting is the most reliable free method to confirm ovulation and understand your cycle. By taking your temperature every morning at the same time and looking for the sustained rise after ovulation, you can pinpoint your fertile window, identify cycle problems, and detect early pregnancy.

Combine BBT with cervical mucus tracking and ovulation predictor kits for the most complete picture of your fertility. After 2-3 cycles of charting, you'll understand your unique patterns and can time intercourse for the best chance of conception.

Related Tools & Resources