How To Calculate Days Past Ovulation (DPO)

Here’s how to calculate days past ovulation (which stands for days past ovulation): the day you ovulate is Day 0. The next day is one day past ovulation or 1DPO. The day after that is two days past ovulation or 2DPO. That means if you ovulated on the second of the month, the 9th of the month would be 7DPO.

You can start taking early pregnancy tests (like First Response) as early as nine days past ovulation, although many tests aren’t sensitive enough to pick up the HCG (pregnancy hormone) in your urine until 14DPO, so don’t get discouraged if that early pregnancy test is negative!

The hardest thing to calculate days past ovulation is just knowing when you ovulated. I’ll walk you through all of the steps to get as close to your ovulation date as possible.

Calendar to show ovulation, days past ovulation (DPO), and when to take a pregnancy take.
Calculate Days Past Ovulation

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What is ovulation?

Ovulation is when your body releases an egg from your ovaries. The egg travels through your fallopian tubes and then to your uterus.

If the egg is fertilized, you may become pregnant. If not, you will have your period.

Truth time: When I was trying to get pregnant with my son, I started reading about fertility and my menstrual cycle, and I was SHOCKED by how little I actually knew about my period and ovulating 😆

I decided that I needed more information on how to get pregnant, so I bought the book “What To Expect Before You’re Expecting” from the best-selling author Heidi Murkoff of “What To Expect When You’re Expecting.”

This book taught me everything I know about my cycle, including ovulation! 

Whether you’re trying to conceive or just trying to learn more about a woman’s body (#womenareamazing), I would encourage you to buy your own copy of this quick read. 

Caclulate (DPO) Days Past Ovulation. Marked Calendar.
How To Calculate Days Past Ovulation (DPO)

What Happens During Ovulation

In a nutshell… 

Or maybe I should say eggshell… Your menstrual cycle has three phases:

  1. The follicular phase: your ovaries prepare one egg to be released.
  2. Ovulation: your body releases an egg from the ovaries, and it travels through the fallopian tubes to the uterus.
  3. The luteal phase: your body prepares for pregnancy by thickening the uterine walls.
  4. Pregnancy begins when the egg is fertilized and implanted; otherwise, you get your period around 14DPO.

Let’s dive a little deeper into the ovulation process.

Women have two ovaries (a right and a left). Your ovaries are full of eggs.  In fact, you are born with all of the eggs that you will ever have! 

Typically, your ovaries take turns releasing the egg, but it doesn’t always happen that way… Nor does it matter!

Ovulation is usually painless, and there aren’t obvious signs to tell you when you ovulate. Some women, like myself, experience cramping during ovulation, also known as Mittelschmirtz.   

What Does Days Past Ovulation Mean?

Whether you are trying to conceive or just trying to understand your menstrual cycle and fertility, you have probably come across the term “Days Past Ovulation” or “DPO.”  

Days past ovulation is simply the number of days that have gone by since the day of ovulation. 

Knowing days past ovulation can be helpful for tracking your fertile window (the days you are most likely to get pregnant) or knowing when you can start taking a home pregnancy test

To calculate days past ovulation, you need to know your ovulation date.  

Calculate DPO (Days Past Ovulation). Marked calendar. Ovulation. Pregnancy test.
How To Calculate DPO (Days Past Ovulation)

How To Calculate Days Past Ovulation 

Calculating days past ovulation is easy!  

The day you ovulate is considered “Day 0,” and each day after that is considered “Day 1,” Day 2,” “Day 3,” etc. 

The hardest part about calculating days past ovulation is figuring out when you actually ovulated! 

Here are five ways to figure out when you ovulated:

  1. Using your cycle
  2. Ovulation calculators and apps 
  3. Physical signs that you’re about to ovulate:
  4. Ovulation predictor kits 

Let’s look at each one more closely.

1. Using Your Cycle To Find Out When You Ovulate 

The average cycle length is 28 days.  Ovulation typically happens 14 days before your period. This method isn’t perfect for determining ovulation, especially if you don’t have a regular cycle.

Your cycle is calculated by counting the days between the first day of your period and the first day of your next period. 

Ovulation typically happens 14 days before your period.  

So, for an average menstrual cycle, this means you will likely ovulate on the 14th day of your cycle.

How Do You Know If You Have A Regular Cycle? 

If your periods usually come at the same time each month, you likely have a regular menstrual cycle. If you are new to tracking your cycle, you might not know if it is always the same (regular).

Grab a calendar and mark the first day of your last period (not the last day of your period!). This is Day 1 of your cycle.

When you get your next period, mark the first day of the period on the calendar again. This is Day 1 of month two. Count how many days are between Day 1 of your first month and Day 1 of your second month. That is the length of your menstrual cycle.

You might have to track a few cycles to know if your period is regular (the same length each month) or irregular (different lengths each month). 

How long is your cycle? Marked calendar. First day of your period. This cycle is 30 days long.
How Long Is Your Menstrual Cycle?

Do I have an irregular menstrual cycle?  

An irregular cycle is a menstrual cycle that has different lengths. Note that I am not talking about the length of your period. I’m talking about the number of days between the first day of one period and the first day of the next.

It is normal for your periods to be longer in some months and shorter in others.  It is also completely normal to have heavier bleeding in some months than in others. The actual amount of days that you are bleeding doesn’t matter.

Pro Tip: Just because your period is different lengths or your flow changes doesn’t mean you have irregular cycles.  

If, after tracking your cycles for a few months, you realize your cycle length is off by a few days or more, you have irregular cycles

You might have irregular cycles from medical conditions, medicines, or breastfeeding (just to name a few).  Sometimes, irregular cycles will become regular again at some point, and some women have chronic irregular cycles. 

It will be more difficult to know when you ovulate if you have an irregular cycle, but not impossible! Read on. 

2. Using Ovulation Calculators And Apps

Ovulation Calculators

There are many websites that will tell you when you likely ovulated, but these calculators only work if you have regular cycles.

Web MD has an Ovulation Calculator and Calendar

This method will require you to know information like when your last period was and how long your cycles are.  These websites can be pretty accurate for people with regular cycles but will not be accurate for those with irregular cycles. 

Ovulation, Period, and Fertility Apps 

Whether you are just tracking your cycle or are trying to conceive, there are several apps on the market that I have personally used that I would recommend.  

  1. Fertility Friend: The app has a lot of features, but it’s not very pretty. I liked it because it offers a free course that explains your cycle in detail and lets you export fertility graphs. 
  2. Premom: Premom stands out from other apps with its user-friendly interface and unique feature that reads your pregnancy tests and ovulation strips. You can take pictures of your tests; the app will tell you if they’re positive.

Premom sells its own ovulation strips and pregnancy tests specifically designed for the app, but you can use ANY kind of ovulation strip or pregnancy test (except for digital ones).  

Personally, I used these Pregmate ovulation strips from Amazon (bonus: you get 20 pregnancy tests, too) and First Response pregnancy tests for both of my babies. 

With both apps, the more information that you log each day, the more accurate their ovulation predictor will be.  

3. Physical Signs That You Are About To Ovulate 

Cervical Mucus

Your body is going to be the most reliable to tell you when you are ovulating if you know what to look for. These are the most accurate of the different methods to find out when you ovulate. 

Pro Tip: To have the best picture of your full menstrual cycle, I would suggest using these physical signs WITH one of the apps listed above to get the most accurate picture of your cycle. 

Cervical mucus is secreted from the vagina throughout your cycle.  It can be watery, sticky, creamy, or have the consistency of egg whites.  

Checking your cervical mucus does not have to be an invasive process.  When you wipe in the bathroom, take note of what type of cervical mucus (if any) is on the toilet paper.  Egg white cervical mucus (EWCM) will happen right before ovulation.  

If you notice that your cervical mucus looks like egg white, you are likely going to ovulate in the next 24-48 hours

Basal Body Temperature

Your basal body temperature (BBT) is your body’s temperature at rest. This is different from a normal temperature because it must be taken first thing in the morning before you even move. You need a special thermometer to take your basal body temperature. Your BBT stays pretty consistent during your follicular phase and will rise 24 hours after you ovulate.   

If you are charting your cycle using one of the apps, you will be able to tell exactly when you ovulated. 

For this reason, charting your cycle for a few months usually reveals a pattern where you can accurately predict when you will ovulate based on previous months.  

Pro Tip: This sounds like the best way to track ovulation, right? There is an exact science to follow… but the downside to this method is that you will be past your fertile peak when you see the spike in temperature (because the spike happens after you ovulate).

Other Physical Signs of Ovulation 

Many women feel physical signs of ovulation the day before or after they ovulate.  

These symptoms are similar to what you experience before or during your period.  

This is not a complete list, but here are some signs of ovulation: 

  • Sore breasts or tender breasts
  • Cramps (sometimes called Middleshmirtz)
  • A twinge or pain on either side of the ovaries (usually right when the egg is released) 

4. Ovulation Predictor Kits 

Besides calendars, charts, apps, and physical symptoms (like cervical mucus, basal body temperature, etc.), an ovulation predictor kit is the best way to know exactly when you are ovulating. 

Ovulation predictor kits (also called OPKs) have the most accurate results because they measure the LH (luteinizing hormone) in your urine.  

These kits will give you definite positive results or negative results.  

There are many ovulation test kits out there… I personally found success with these Pregmate strips. The directions were clear, and I always got a positive result before ovulation.  

Plus, when used as directed, you could be using 2-3 strips a day as you get closer to your ovulation date, so they are very easy on the wallet compared to other tests.  

One of the drawbacks to testing kits with a control and test line is it might be difficult to tell if something is positive, negative, or somewhere in between.  

If you want to take the guesswork out completely, you can buy a digital ovulation predictor kit (OPK).  These kits will tell you when you are about to ovulate.  

For all OPK tests, ovulation will happen within 36 hours of receiving a positive test.  

Here’s a quick recap of the four ways to track ovulation:

  1. Based on your regular cycle, you will ovulate 14 days before your period.
  2. Use a calculator or app for even more insights (although they are most reliable for regular periods).
  3. Check your cervical mucus when you wipe, and be on the lookout for egg white cervical mucus (EWCM) 24-48 hours before you ovulate.
  4. The best way to know exactly when you ovulate is using your basal body temperature (BBT). Unfortunately, you will miss your fertile window by tracking ovulation this way.  
  5. Use an OPK to give you a specific 36-hour window of when you will ovulate.  

Ovulation And Trying To Conceive 

If you are trying to conceive, you need to have sex within 24 hours of ovulating. This is because your egg is only viable for 24 hours. Knowing when you ovulate is so important for getting pregnant.

you should chart your cycle and give it six months to a year of actively trying to get pregnant before you sound the alarm bells.  

While I can’t say that knowing when you ovulate will get you pregnant any faster, if you don’t know, you will be leaving it all up to chance.

When is your fertile window? Marked calendar. Ovulation. Most fertile days.
When Is Your Fertile Window?

Ovulation and Your Fertile Window

Your fertile window is the five days before ovulation and ovulation day itself (6 days total).

You might be wondering why your fertile window is six days when your egg is only viable for 24 hours. Good question!

Your egg is only viable for 24 hours, but sperm is viable for five days. That means you should start having sex for the five days leading up to ovulation and ovulation day itself.

Fertility charting will give you the best chance of catching your fertile window.  

Can You Get Pregnant When You’re Not Ovulating?

Yes.  When you have sex, the sperm travels to the fallopian tubes. The sperm can live for up to 5 days inside the fallopian tubes.  Because of this, you can get pregnant for five days before ovulation and the day of ovulation itself. 

When Should You Take A Pregnancy Test? 

Most pregnancy tests are not going to be accurate until the day of your missed period.  More sensitive tests are on the market now, like the Family First 6 Days Sooner tests that will detect HCG around 8 DPO.  I got both of my positive pregnancy tests at 8 DPO with these tests. 

Home pregnancy tests measure the human chorionic gonadotropin (HCG) in your urine.  HCG increases as your baby grows but typically cannot be detected in over-the-counter tests until 14 days after ovulation.  

You should talk to your healthcare provider if you need to determine pregnancy before 8 DPO.  They may be able to do a urine test or blood test that is more sensitive to detect pregnancy.  

What Happens After Ovulation?

After ovulation, one of two things happens: 

  1. You get your period.
  2. You are pregnant. 

You won’t know either right away.  Immediately after ovulation, your body goes into the luteal phase.  Think of this as your body’s natural “waiting period.” The luteal phase is around 14 days long. Here’s what happens:

  1. If the egg is fertilized, it will start producing progesterone, which tells your body not to shed the uterine lining. Congrats! You are pregnant! 
  2. At the end of each menstrual cycle, if the egg is not fertilized and no progesterone is detected, your body will automatically shed the uterine lining, resulting in what we know as a period! 

Women’s bodies are amazing 😊! 

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Hi, I'm Jacqui, founder of Mommy Maker Teacher and mom of two toddlers. With a degree in education, 12+ years of experience as a K-12 teacher and curriculum developer, and courses in childhood psychology and language acquisition, I share research-backed parenting tips and advice. I provide helpful content for moms on all stages of motherhood - from trying to conceive and pregnancy to postpartum, breastfeeding, and parenting.