Ovulation “prediction” sounds straightforward—until you look at real cycles. Many popular apps lean on calendar math, but ovulation varies by person and by month. Below is what independent studies and guidelines say, where tracking goes wrong, and practical (evidence-based) ways to time intercourse without overcomplicating your life.
What the research actually says
Key takeaways from recent evidence:
- Calendar-based app predictions are often inaccurate. Independent evaluations have found wide variation in quality and poor day-level accuracy for many consumer apps that don’t use biological markers.1–3
- Urine LH tests (OPKs) better identify the fertile window because they detect the luteinizing hormone surge that precedes ovulation, though ovulation can occur a day or so after the first positive and timing still varies.4–6
- Basal body temperature (BBT) rises after ovulation—helpful for confirming that ovulation happened, but not great for predicting it in advance.4,6
Why predictions miss the mark
- Cycle variability: Even in “regular” cycles, the follicular phase length can shift; stress, illness, travel, and postpartum changes all move ovulation earlier or later.
- Algorithm limits: Many apps infer the fertile window from prior cycles instead of measuring current biology.
- Human factors: Interpreting mucus/BBT requires training and consistency; mixed methods without a plan can add noise.
What works better (practical plan)
- Time intercourse every 1–2 days during the fertile window. This simple schedule avoids the need to pinpoint the exact day and is endorsed by leading guidelines.4,6
- Use urine LH tests to open the window (first positive = start or continue every-other-day timing for a few days). Don’t overtest—keep it simple.
- Use tools for planning & expectations—not just prediction. A calendar of daily chances can help you plan without obsessing over a single “ovulation day.”
Estimate your fertile window and plan timing—no app sorcery needed.
See daily conception odds across your cycle (useful with or without LH tests).
FAQ
Are ovulation apps accurate?
It depends. Apps that rely on past cycle lengths (without biological signals) often miss the exact fertile days. Studies evaluating consumer apps have documented substantial inaccuracies in predicted ovulation dates.1–3
Are LH tests better?
Generally yes. Home urine LH kits detect the LH surge that precedes ovulation and can improve timing. Still, the surge-to-ovulation interval varies and false starts occur, so pair tests with a simple every-other-day schedule.4–6
How often should we have sex when trying?
Guidelines suggest intercourse every 1–2 days during the fertile window. Daily is fine if preferred; every other day is usually easier and equally effective for most couples.4,6
Sources
- Moglia ML, Nguyen HV, Chyjek K, Chen KT, Castaño PM. Evaluation of smartphone menstrual cycle tracking applications using an adapted APPLICATIONS scoring system. Obstet Gynecol. 2016;127(6):1153–1160. Journal link
- Earle S, Marston HR, Hadley R, Banks D. Use of menstruation and fertility app trackers: A scoping review of the evidence. BMJ Sex Reprod Health. 2021;47(2):90–101. DOI
- Freis A, Freundl-Schütt T, Wallwiener M, et al. Prediction of the fertile window by tracking menstrual cycles: comparison of a digital fertility tracker with basal body temperature. Eur J Contracept Reprod Health Care. 2018;23(1):45–52. Journal link
- ASRM Practice Committee. Optimizing natural fertility in couples trying to conceive. Fertil Steril. 2017 (reaffirmed 2022). ASRM overview
- ACOG. Planning for Pregnancy / Patient guidance on timing intercourse and ovulation testing. ACOG
- NICE. Fertility problems: assessment and treatment (NG201) – timing and lifestyle considerations. NICE Guideline
This article summarizes peer-reviewed studies and major guidelines. It is for education only and is not medical advice.