The question of whether the chance of getting pregnant increases each month is common for couples actively trying to conceive (TTC). While the underlying monthly rate of conception (fecundability) generally remains consistent for a healthy couple, the overall probability of eventually achieving pregnancy increases with each passing month of trying. This distinction between the single-cycle rate and the cumulative success rate is important for understanding the realistic timeline for conception.
Understanding Monthly Fertility Rates
For healthy couples under the age of 35, the chance of achieving pregnancy in any single menstrual cycle is approximately 20% to 25%. This rate does not statistically improve simply because the couple failed to conceive the month before. It is similar to flipping a coin, where the odds of landing on heads remain 50% on the next flip, regardless of the previous outcome.
This individual cycle rate is highest when the woman is in her 20s and begins to decline gradually in the early 30s. By age 40, the monthly chance drops significantly, falling to 5% or less per cycle. The 20% to 25% figure serves as the statistical starting point for couples with no known fertility issues.
The Cumulative Nature of Conception
While the monthly rate itself does not increase, the overall probability of success grows substantially over time due to the compounding of chances. This is the concept of cumulative probability. Each month provides another independent opportunity to achieve pregnancy, adding to the total likelihood of conception within a given period.
For a healthy couple, the cumulative success rate increases significantly over time:
- Approximately 50% will conceive within the first three months of trying.
- This figure rises to about 70% to 75% after six months of consistent trying.
- By the end of one year, the cumulative success rate reaches about 85%.
- Over 90% of couples eventually conceive after two years of trying.
Key Factors That Influence Your Monthly Odds
The baseline monthly rate of 20% to 25% is heavily modified by biological and behavioral factors. Maternal age is the most significant determinant, as both the quantity and quality of a woman’s eggs decline as she gets older.
Cycle regularity is another major factor because conception hinges on accurate timing of intercourse around ovulation. The fertile window is only about six days long, ending on the day of ovulation, with the highest probability occurring in the two days prior. Couples who time intercourse accurately within this window have significantly higher monthly success rates. Lifestyle factors such as smoking, extreme weight, and certain underlying health conditions can also reduce the monthly probability of conception.
Practical Timeline for Trying to Conceive
Based on cumulative statistics, medical professionals have established clear guidelines for when to seek professional evaluation.
Guidelines for Seeking Evaluation
Women under the age of 35 are generally advised to try to conceive for 12 months before consulting a fertility specialist.
For women who are 35 years of age or older, the recommended period for trying is shortened to six months. This accelerated timeline is due to the age-related decline in both egg quality and quantity, which makes early intervention more beneficial. Women over 40 may be encouraged to seek an evaluation almost immediately.