Ovulation Calculator

Find your most fertile days and estimated ovulation date from your last period and cycle length. Free, instant, no signup.

How to use the Ovulation Calculator

  1. Enter your values. Fill in the fields with your numbers.
  2. Calculate. Press Calculate to run the ovulation calculator.
  3. Use the result. Copy the result or try a related tool next.

Why use our Ovulation Calculator

Instant results. Enter your figures and the ovulation calculator returns an answer in seconds.
Free & private. Runs in your browser — no signup, and nothing is sent to a server.
Accurate. Uses standard formulas so you can rely on the numbers.

Free to use — premium coming soon

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  • No signup
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About the Ovulation Calculator

The Ovulation Calculator estimates the days in your cycle when you are most likely to conceive, using just two inputs: the first day of your last menstrual period and your average cycle length. From these it counts forward to project your next period, then works backward to mark your probable ovulation day and the surrounding fertile window. It is built for anyone tracking their cycle to try for a baby, time intercourse, or simply understand their own rhythm month to month without needing apps, thermometers, or test strips.

Use it at the start of a new cycle, once you know the date your period began. If you are trying to conceive, the calculator highlights the roughly six-day fertile window so you can plan ahead, since the days just before ovulation are the most likely to result in pregnancy. It is also useful if your cycle is shorter or longer than the textbook 28 days, because it adapts the ovulation estimate to your actual cycle length rather than assuming everyone ovulates on Day 14.

The method rests on the luteal phase, the span between ovulation and your next period, which stays fairly stable at about 12 to 16 days for most people. The calculator subtracts roughly 14 days from your projected next-period date to pinpoint ovulation, then adds the five days before it (to allow for sperm surviving in the reproductive tract) plus ovulation day itself to form the fertile window. A mature egg only lives about 12 to 24 hours, so timing intercourse before ovulation matters more than after.

Treat the results as an informed estimate, not a guarantee. Ovulation can shift by a few days even in regular cycles and is harder to predict if your periods are irregular, so the dates are a starting point rather than a fixed appointment. This tool runs entirely in your browser: the period date and cycle length you type in are used only to do the math on your device and are never uploaded, stored, or shared. For contraception decisions or fertility concerns, confirm timing with a clinician or ovulation tests.

Frequently asked questions

How does the ovulation calculator figure out my ovulation day?

It projects your next period by adding your cycle length to your last period start date, then counts back about 14 days to estimate ovulation. This works because the luteal phase between ovulation and your next period is fairly constant, while the first half of the cycle is what varies.

What is the fertile window and why is it six days?

The fertile window is the five days leading up to ovulation plus ovulation day itself. It spans six days because sperm can survive up to about five days in the reproductive tract while the egg is only viable for roughly 12 to 24 hours after release.

Is the calculator accurate if my cycles are irregular?

It is most reliable for regular cycles. If your cycle length changes a lot from month to month, the estimated ovulation day can be off by several days, so pairing it with ovulation predictor kits or basal body temperature tracking gives a clearer picture.

Do I always ovulate on Day 14?

No. Day 14 only applies to a textbook 28-day cycle. The calculator adjusts ovulation to your own cycle length, so a 30-day cycle points to around Day 16 and a 35-day cycle to around Day 21.

Can I use this as birth control?

It is not designed for contraception. Because ovulation can shift even in regular cycles, relying on predicted infertile days carries a real risk of pregnancy. Use a proven contraceptive method and treat this tool only as a conception-planning aid.

From our blog

From Step Count to Calorie Count: How to Read Your Daily Walking Numbers

By the Super Simple Digital Tools Team · Updated June 2026

Most people glance at a step total and have no idea what it means in energy terms. A pedometer that reads 8,247 is just a number until you connect it to your body, your pace, and the distance you actually covered. Converting steps to calories is the missing translation layer that turns a count into context, telling you whether today's walking was a light contribution or a meaningful chunk of your daily output.

The conversion rests on two ideas. The first is distance: your steps are multiplied by your stride length, which is closely tied to height, so a taller person covers more ground in the same number of steps. The second is intensity, captured by the MET value of walking. A MET expresses how hard an activity is relative to sitting still, and walking ranges from about 2.8 for a slow amble to 5.0 for a brisk march. Combine distance, pace, time, and body weight and you arrive at a calorie figure.

To do it yourself, estimate your stride as your height in metres times 0.414, multiply by your steps to get distance, then divide by your walking speed to get minutes. Plug those minutes into calories equals minutes times MET times 3.5 times weight in kilograms divided by 200. It is a fair bit of arithmetic, which is exactly why a calculator helps; you supply four honest inputs and the tool handles the chain of multiplication without rounding errors creeping in.

The single most important thing to get right is pace, because it shifts the MET value and therefore the entire result. Many people overestimate how fast they walk and inflate their burn. Be honest: if you were strolling and chatting, that is slow or average, not brisk. The same goes for your weight, which should reflect your current number rather than a goal weight, since the formula multiplies calories directly by it.

Finally, use the figure for what it is good at. The MET approach gives a consistent, comparable estimate, but no formula can see hills, headwinds, or your personal metabolism. The smart move is to keep your inputs steady and watch the trend over weeks rather than fixating on a single day's number. Used that way, a steps-to-calories estimate becomes a reliable compass for building a walking habit, not a false promise of precision.

  • Measure your real stride once by walking 10 steps along a tape measure and dividing the distance by 10, then compare it to the height-based estimate for a more personal result.
  • Pick the pace that matches how you actually felt, not how fast you wish you walked; choosing brisk when you strolled can overstate your burn by a third.
  • Enter your current body weight rather than a target weight, since calories scale directly with the weight you put into the formula.
  • Run the same inputs each day and track the trend over a week or two; the estimate is far more useful as a relative measure than as an absolute calorie count.

Read the full guide →

Tool by the Super Simple Digital Tools Team. Reviewed by our editorial team. Free to use, no signup required.

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