Fertility isn’t a simple yes-or-no status. It exists on a spectrum, and most people can get a reasonable picture of where they stand by combining at-home body tracking with targeted blood work. A woman in her early to mid-20s has roughly a 25 to 30% chance of conceiving in any given month, while by age 40 that number drops to about 5%. Those numbers reflect population averages, though. Your individual fertility depends on whether you’re ovulating regularly, how many eggs you have in reserve, whether your reproductive anatomy is clear of blockages, and several other factors you can actually measure.
Track Your Cervical Mucus
One of the simplest and most reliable ways to gauge fertility on any given day is to check your cervical mucus. The fluid your cervix produces changes dramatically throughout your cycle in response to hormone shifts, and those changes tell you whether your body is approaching ovulation.
In the days after your period, mucus is typically thick, white, and dry or sticky, almost paste-like. As you move closer to ovulation, it becomes creamy and smooth, similar to yogurt. Then, right before ovulation, it shifts to wet, watery, and clear. At your most fertile point, the mucus looks and feels like raw egg whites: slippery, stretchy, and slimy. This type of mucus helps sperm travel through the cervix and survive longer in the reproductive tract. After ovulation passes, mucus returns to thick and dry.
If you consistently see that egg-white pattern each cycle, it’s a strong signal your body is gearing up to ovulate normally. If your mucus never becomes slippery or stretchy, or if you experience persistent dryness, it may indicate irregular or absent ovulation.
Monitor Your Basal Body Temperature
Your resting body temperature rises slightly after ovulation due to the hormone progesterone. The increase is small, typically less than half a degree Fahrenheit, but it follows a predictable pattern. Some people see a rise as little as 0.4°F while others see up to 1°F. To catch this shift, you need to take your temperature first thing in the morning before getting out of bed, using a thermometer sensitive to tenths of a degree.
The key limitation: the temperature rise confirms ovulation already happened, so it’s more useful as a retrospective check than a real-time fertility signal. After tracking for two or three cycles, though, you’ll start to see your personal pattern and can predict roughly when the shift will come. A consistent temperature rise each cycle is good evidence that you’re ovulating. If your chart stays flat month after month with no detectable shift, that warrants further investigation.
Use Ovulation Predictor Kits
Over-the-counter ovulation predictor kits (OPKs) detect a surge in luteinizing hormone (LH) in your urine. This surge is the trigger that tells your ovary to release an egg. Ovulation typically occurs 12 to 48 hours after a positive test, with most people ovulating within 8 to 20 hours of the actual LH peak.
Since sperm can survive 3 to 5 days inside the uterus and fallopian tubes, your total fertile window in any cycle is roughly six days: the five days before ovulation plus the day of ovulation itself. A positive OPK tells you you’re in the most fertile part of that window. Consistently getting positive results each cycle is reassuring. If you test through your entire cycle without ever detecting a surge, it could mean you’re not ovulating or that the kit isn’t capturing your particular LH pattern (some people have short surges that are easy to miss).
Blood Tests That Measure Fertility
Body tracking gives you useful clues, but blood work provides more precise data. Three tests are especially informative.
FSH (Follicle-Stimulating Hormone)
This blood draw is done on day 3 of your cycle and measures how hard your brain is working to stimulate your ovaries. Lower levels are better. Under 6 is considered excellent, 6 to 9 is good, 9 to 10 is fair, and anything above 10 suggests diminished ovarian reserve, meaning fewer eggs remain. Levels above 13 indicate the ovaries will be very difficult to stimulate, even with fertility medications.
AMH (Anti-Müllerian Hormone)
AMH gives a snapshot of your egg supply and can be drawn on any day of your cycle. Unlike FSH, it doesn’t fluctuate much from month to month, which makes it a more stable marker. Typical values decline with age: around 3.0 ng/mL at age 25, 2.5 at 30, 1.5 at 35, 1.0 at 40, and 0.5 at 45. These are lower-end estimates, so many people will have values above these numbers. A result significantly below the expected range for your age suggests a lower-than-average egg reserve.
Progesterone
A progesterone test drawn about seven days after ovulation confirms whether ovulation actually occurred and how robust it was. After the egg is released, the empty follicle produces progesterone. A level above 5 ng/mL indicates some ovulatory activity, but most doctors look for a level above 10 on an unmedicated cycle. Below that threshold, ovulation may have been weak or incomplete, which can make it harder for a pregnancy to establish itself.
Structural Tests for Reproductive Anatomy
Even with perfect ovulation and a healthy egg supply, conception requires that sperm and egg can physically meet. A hysterosalpingogram (HSG) is an X-ray procedure that checks for this. A dye is injected through the cervix, and a series of images tracks whether it flows freely through both fallopian tubes and spills out the ends. If the dye meets a barrier, one or both tubes are blocked. The test can also reveal irregularities in the shape of the uterus, some of which can interfere with implantation or pregnancy.
An HSG isn’t typically a first-line test. It’s usually ordered after initial blood work or after you’ve been trying to conceive without success. The procedure takes about 10 to 15 minutes and can cause cramping similar to period pain, but it provides information no blood test or at-home method can.
How Age Affects Your Fertility Timeline
Age is the single strongest predictor of natural fertility, and the decline is steeper than most people expect. In your early to mid-20s, the monthly probability of conception is 25 to 30%. By 40, it’s around 5%. The drop isn’t just about egg quantity. Egg quality also decreases over time, which raises the risk of chromosomal abnormalities and makes each individual egg less likely to result in a viable pregnancy.
This doesn’t mean conception after 35 or 40 is impossible. It means the timeline is shorter and the margin for other fertility issues is narrower. A blocked tube or mildly low progesterone at 27 might not matter much because you have many cycles ahead with good odds. The same issue at 39 becomes more significant because each cycle carries lower baseline odds.
When the Timeline Suggests a Problem
The American College of Obstetricians and Gynecologists recommends a formal fertility evaluation if you haven’t conceived after one year of regular, unprotected intercourse. If you’re over 35, that window shortens to six months. If you’re over 40, the recommendation is to seek evaluation right away rather than waiting.
Certain signs also warrant earlier investigation regardless of age: periods that are very irregular or absent, cycles shorter than 21 days or longer than 35, a known history of pelvic inflammatory disease or endometriosis, or a partner with a known reproductive health issue. For men, a semen analysis is a straightforward test that checks sperm count, motility, and shape, and it’s typically part of any initial fertility workup since male factors contribute to roughly half of all cases of difficulty conceiving.