How do you calculate your luteal phase?
Your luteal phase starts the day after you ovulate and ends when your next period starts. Count the days in between. If you ovulated on October 3 and your period came on October 17, your luteal phase ran from October 4 to October 16, which is 13 days.
If you think in cycle days, take the day you ovulated away from your cycle length. Ovulation on day 16 of a 30-day cycle gives you a 14-day luteal phase.
How long is the luteal phase supposed to be?
Cleveland Clinic puts the average at 12 to 14 days. Anything from 10 to 17 days is normal.
| Luteal phase | What it means |
|---|---|
| Under 10 days | Short. Your period comes within 10 days of ovulation, which may not give the lining of your uterus long enough to thicken. |
| 10 to 17 days | Normal. Most people land on 12, 13 or 14. |
| 18 days or more | Long. Pregnancy is the first thing to rule out. A hormone imbalance can also do it. |
Cleveland Clinic suggests a pregnancy test if your period hasn’t come within 14 days of ovulation. If your cycles vary and you can’t tell when it was due, the pregnancy test calculator gives you a date.
How to calculate your luteal phase without knowing ovulation
You can’t measure it without a sign of ovulation, but you can make a fair guess. Because the luteal phase changes so little, period apps count back from your next period to find ovulation. The calculator does the same when you leave the dates blank. These are the numbers it uses.
| Cycle length | Luteal phase | Likely ovulation |
|---|---|---|
| 24 days | 12 days | Day 12 |
| 26 days | 14 days | Day 12 |
| 28 days | 14 days | Day 14 |
| 30 days | 14 days | Day 16 |
| 32 days | 14 days | Day 18 |
| 35 days | 15 days | Day 20 |
Don’t know your cycle length? The cycle length calculator works it out from a few period start dates.
How do I know which day I ovulated?
Ovulation tests are the easiest way. They pick up the hormone surge that comes before the egg is released, so ovulation is usually the day after your first positive test. A thermometer works too. Your temperature when you wake up rises by about 0.4°F (0.2°C) after you ovulate and stays up until your period, so the last low day before the rise is your best guess. Discharge helps as well. It’s wet and slippery around ovulation and turns thick and pasty in the luteal phase.
Two signs that agree are better than one. If you’re still working out roughly when to start testing, count from your period date.
What does a short luteal phase mean?
A luteal phase under 10 days means your period comes soon after ovulation. The lining of your uterus has less time to thicken, so it can make getting pregnant harder. One short cycle on its own isn’t much to go on, because counting mistakes and an unusual month both happen. If you’re trying to conceive and it shows up cycle after cycle, take your dates to a doctor. If you’re not trying, a short luteal phase usually isn’t something you’d notice.
Keeping track in Plum
Plum, a period tracker app for iPhone, lets you log ovulation tests as positive, negative or unclear on the day you take them. With your period start dates already saved, the days between a positive test and your next period are on the calendar when you want to count them. Plum’s predictions don’t use your tests yet. They count back from your cycle length, like this calculator does when you leave the dates blank.
