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Calcolatore Temperatura Basale (BBT)

Confirm ovulation and check your biphasic thermal shift using the clinical Sympto-Thermal 3-over-6 rule. Plot waking temperatures and calculate your coverline instantly.

Quick Summary: 3-Over-6 Sympto-Thermal Rule

To clinically confirm ovulation via Basal Body Temperature (BBT), you must observe 3 consecutive days with waking temperatures at least 0.4°F (0.2°C) higher than the highest of the preceding 6 consecutive days. The horizontal coverline is drawn 0.1°F (0.05°C) above that 6-day follicular high.

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Modello Computazionale Basato su Evidenze • Revisionato a Ottobre 2026

Revisionato da: Team di Ricerca Clinica e Metodologia Computazionale di Free Ovulation Tracker

Letteratura Primaria di Riferimento: Wilcox et al. (NEJM, 1995 & 1999) • Bollettini di Pratica ACOG • Standard di Salute Riproduttiva OMS

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Daily Waking Temperature Entries

Enter 10 to 14 consecutive waking temperatures to detect your thermal shift.

Ovulation Confirmed on Cycle Day 6 (Thermal Shift on Day 7). Sympto-Thermal Rule Met: sustained rise (≥ +0.4°F). Calculated coverline: 97.7°F.

Biphasic Temperature Curve--- Coverline: 97.7°F

Daily Waking Temperature Entries (°F)12 Days

Day 1

Day 2

Day 3

Day 4

Day 5

Day 6

Day 7Thermal Shift

Day 8

Day 9

Day 10

Day 11

Day 12

Combine BBT with Calendar Forecasts for Precision Timing

BBT temperature shifts confirm ovulation retrospectively after the egg has already released. To predict your 6-day fertile window in advance, cross-reference with our primary calculator.

Free Ovulation Tracker

Clinical Methodology

How Progesterone Drives the Basal Body Temperature Shift

Basal body temperature (BBT) is the lowest natural resting body temperature measured immediately upon waking, before any physical movement, speaking, or drinking. During the follicular phase, systemic circulating estrogen dominates, keeping basal temperatures in a lower range (97.0°F–97.7°F or 36.1°C–36.5°C).

Immediately following ovulation, the collapsed ovarian follicle reorganizes into the corpus luteum, which synthesizes progesterone, elevating resting metabolic rate and raising temperatures by 0.4°F to 0.8°F (0.2°C to 0.5°C). Pair with our primary ovulation calculator to pinpoint your fertile window in advance.

Frequently Asked Questions About BBT Charting

Audited under our Clinical Methodology & Citations.

What is the 3-over-6 rule in basal body temperature (BBT) charting?

The 3-over-6 rule is the clinical Sympto-Thermal standard: ovulation is confirmed when you record 3 consecutive waking temperatures at least 0.2°C (0.4°F) higher than the highest of the preceding 6 consecutive days.

How do you calculate the BBT coverline?

Identify the highest of the 6 follicular temperatures immediately preceding the thermal shift and draw a horizontal line 0.1°F (or 0.05°C) above that peak temperature.

Can BBT predict ovulation before it happens?

No. Basal body temperature rises only after progesterone enters circulation following egg release. Because the egg lives only 12 to 24 hours, waiting for a temperature rise means the fertile window has already closed.

What causes a stepped thermal shift instead of a sharp spike?

In roughly 15–20% of ovulatory cycles, corpus luteum progesterone ramps up gradually over 2 to 3 days rather than spiking overnight. As long as temperatures remain above the coverline, the cycle is ovulatory.

Primary Fertility Hub