When to Take a Pregnancy Test on a 37-Day Cycle
On a 37-day cycle, the most reliable time to take a home pregnancy test is cycle day 38, the day your next period is due. Some sensitive tests may pick up a pregnancy a few days earlier, from around cycle day 33.
| Cycle length | 37 days |
|---|---|
| Likely ovulation day | Cycle day 23 (range 21–25) |
| Fertile window | Cycle days 18–23 |
| Most fertile days | Cycle days 21–23 |
| Next period due | Cycle day 38 |
Why you can't test straight away
Pregnancy tests detect hCG, a hormone that only starts to be made after the embryo implants, usually 6 to 12 days after ovulation. Levels then roughly double every couple of days, so testing too early can give a negative result even if you are pregnant.
If the test is negative
If your period still hasn't arrived, test again in two to three days. If you keep getting negatives and your period is more than a week late, a doctor can check for other causes.
Cycles longer than 35 days fall outside the typical adult range of 21 to 35 days. Long or unpredictable cycles can be a sign that ovulation isn't happening every month, for example with polycystic ovary syndrome (PCOS) or thyroid problems. If your cycles are regularly 37 days or longer, it's worth talking to a doctor, especially if you're trying to conceive.
Pregnancy Test Date Calculator: Find the earliest and the most reliable days to take a pregnancy test.
Open the calculatorThis article is general information, not medical advice. Talk to a doctor or midwife about your own pregnancy or fertility.