Helping You Monitor Your Fertility

Recommended Pages for Further Reading


"Even though software can automate analysis, couples can still benefit from understanding how to interpret their charts and estimate fertility and ovulation."


Ovulation Calendar


There are numerous techniques that can be applied to analyze symptothermal data. Some common methods are described here. Readers should also check the symptom pages for more information about recording individual symptoms.

Everyone can benefit from learning to interpret their fertility. At first it can be overwhelming though. Fertility software may help simplify the initial learning curve. It can interpret your symptoms and calculate ovulation for you. This can help couples get accustomed to how fertility awareness works as they learn to interpret their own charts to complement the software's analysis.

Electronic charting tools that offer chart shading can help couples learn how to interpret their charts. The following manual steps are also explained in detail below.

Cervical Mucus Analysis

Cervical mucus observations have intrinsic fertility information associated with them. For example, stretchy mucus is a sign of fertility and a high chance of getting pregnant. Mucus that breaks easily and does not stretch suggests low fertility. Individual symptoms already suggest fertility.

Beyond considering the individual day to day values, cervical mucus can also be interpreted by looking at data collectively throughout the cycle.

Early in the cycle only the first days with infertile mucus symptoms are considered to have a low pregnancy risk (assuming other symptoms or cycle history does not justify start of the fertile window sooner). These are the days labeled with the letter D on the chart. Once the first fertile characteristic (M or S) are recorded on the chart, the chances of getting pregnant are no longer considered small. The remainder of the cycle is not considered safe to resume intercourse until after ovulation for couples trying to postpone pregnancy.

The last day with fertile characteristics (S on the chart) is estimated to be the day of ovulation. For couples trying to conceive, this is the optimum time to plan intercourse. The days that immediately precede this date also have very good potential for pregnancy. Couples interested avoiding pregnancy should wait 4 days after the last recorded fertile symptom before assuming that the likelihood of conception subsided. Cycle history and other symptoms can also be used to decide when the fertile window is estimated to end.

Basal Body Temperature Analysis

There are many ways to interpret basal body temperature data. Two methods are described here. The simplest is the coverline approach. This establishes a baseline temperature early in the cycle and requires this baseline to be crossed later in the cycle to confirm ovulation. The other approach uses the three over six rule to estimate ovulation. This is a more involved method.

The coverline technique first establishes a coverline early in the cycle. This can be established using several different rules. One approach sets the coverline temperature to be 0.15 degrees higher than the highest temperature recorded during the first ten days of the cycle (add only 0.08 degrees instead if charting temperatures on the Celsius scale). Another approach uses temperature data from the previous cycle (Vollman technique). All temperature values from the prior cycle are averaged to arrive at an average temperature. The coverline is set at this temperature.

Once a coverline temperature is determined, a horizontal line is drawn across the chart at this temperature. This line is called the coverline. With this line established, interpretation involves waiting for the temperature data to exceed and remain above the coverline. The crossing of the coverline indicates that ovulation has taken place.

The three over six rule similarly creates a base temperature that must be exceeded, but it sets this base temperature more dynamically. As was described on the BBT page, this technique requires that three or four temperatures be higher than the prior six temperatures. To think in terms of the coverline approach, the coverline temperature is set at 0.2 degrees Fahrenheit (or 0.1 degrees Celsius) above the highest of the prior six temperatures. Ovulation can be confirmed once 3 temperatures are above the coverline assuming one of the three temperatures is an additional 0.2 degrees above the coverline (0.4 degrees above the highest temperature point). If three temperatures are above the coverline but none are an additional 0.2 degrees above it, then you should wait for a fourth day to be above the coverline before concluding that ovulation occured.

Ovulation can be calculated using the three over six rule. Like the coverline technique, it can only identify ovulation after it has already occurred. This information arrives too late for couples trying to conceive. Knowing that ovulation occurred and looking for patterns from cycle to cycle can still make BBT worthwhile for couples interested in pregnancy. Those trying to avoid pregnancy should hold off until ovulation is confirmed before assuming that fertility levels have subsided. If multiple symptoms are tracked, you should wait until all symptoms have confirmed that the fertile window has ended.

Ovulation Test Results

LH ovulation tests identify the LH surge associated with ovulation. Once a positive test is recorded, ovulation can be expected within the next 24-36 hours. This means that the 1-2 days after receiving a positive ovulation test result will offer the best chances for conception.

Ovulation kits come with instructions that explain how an individual test should be used and interpreted. Refer to these instructions from the specific test you are using for more information.

Software Analysis

Knowing how to manually interpret fertility and predict ovulation is useful. It can be difficult to learn at first though. To help ease this learning phase, couples may wish to consider charting software. Fertility software can help interpret ovulation and fertility for you.

Even though software can take care of all analysis and calculations, couples may still wish to consider learning to interpret fertility symptoms themselves. This can be useful to check the software calculations. Your assessment can sometimes offer a different perspective and allow you to further speculate on and understand your fertility.