“My app tells me when I ovulate”. I hear this on the daily, but here’s the thing, your app predicts ovulation and your fertile window based on math, not on your actual body. Apps guesstimate your ovulation and fertile window based on your past monthly patterns, which don’t influence your current cycle.

The deets

The second half of our monthly cycle, from ovulation to the next period, is called the luteal phase and lasts about 12-16 days pretty consistently. But the follicular phase, from the first day of a period to ovulation, can be fickle. Ovulation can be delayed by stress, travel, moving, illnesses, medications, strenuous exercise, and sudden weight changes, and an app can’t predict that. This is why when we might have a late period when we’re going through a particularly stressful time in life - the follicular phase was longer than usual, ovulation was late, and so the period is late.

The fix

So if your app can’t tell you the whole story what’s the most accurate way to track your fertile window? Charting your your basal body temperature (BBT) and cervical fluid! BBT tells you that you did ovulate, when it happened, and if the luteal phase is long enough for you to get pregnant. Cervical fluid changes from dry to slippery the closer you get to ovulation. Read more about how to get started charting your cycles here.