Free ovulation calculator
Your fertile window, worked out honestly.
Put in the first day of your last period and see when you're most likely to ovulate, with the range a real estimate has. Then, if you like, keep going: CycleHelm learns your pattern and tells you what's coming each cycle, and each week once you're pregnant.
The first day of bleeding, not spotting.
From the first day of one period to the day before the next. 28 is an average; anywhere from 21 to 35 is common.
A calculator gives you a date. Then nothing.
You come back next month and type it all in again. It never learns that your cycles run long, or that you ovulated late last time, and it never says how sure it is.
CycleHelm starts from the same calculator and keeps going. Log your period when it comes and it learns your real cycle. Get a positive test and it follows the pregnancy week by week, with the visits that are coming and what to ask at each.
- 1Work it outAny calculator, no account. Your inputs stay on your device.
- 2Keep itSave it to a private account and log your next period when it comes.
- 3It learnsYour real cycle length, how much it moves, and your luteal phase from your tests.
- 4It tells youA heads-up before your window, or each pregnancy week, and what to ask at each visit.
Honest ranges, from your own cycles
Every date shows the likely day and how far it could move. With your history, the range comes from how much your cycles actually vary, and your ovulation tests teach it your luteal phase. When your cycles vary a lot, it says so plainly, and says when that's worth mentioning to a clinician.
Window opens tomorrow
Day 12
- Fertile window
- Mar 14 to 19
- Ovulation
- Around Mar 19
- Mar 17 to Mar 21
- Based on
- Your last 7 cycles (29 to 31 days) and the 13-day luteal phase your tests showed.
Pregnancy, one week at a time
Set your due date from your last period, a scan, an IVF transfer or the date your clinician gave you. Each week you'll see what's developing, what's changing for you, what's worth doing, and the routine visits coming up, with a short email when each new week starts.
19 weeks, 0 days
148 days to go. Second trimester.
First
to Feb 18
Second
to May 27
Third
due Aug 20
About the size of a mango
A creamy coating called vernix is forming to protect the skin.
This week
If you're working, look at your employer's parental leave paperwork timeline
Walk into appointments ready
Each visit comes with the questions worth asking at that stage, and you add your own. One printable page puts your cycle lengths, period lengths, positive tests, months trying and due date in front of your clinician, so you're not scrolling through screenshots in the exam room.
Cycle and pregnancy summary
- Typical cycle
- 30 days (29 to 31)
- Luteal phase
- 13 days, from tests
- Trying since
- Jun 2026 (about 9 months)
| Started | Cycle | Period | Positive test |
|---|---|---|---|
| Jan 4 | 29 days | 5 days | cycle day 16 |
| Feb 2 | 31 days | 4 days | cycle day 18 |
| Mar 5 | 30 days | 5 days | cycle day 17 |
Questions
- Would blood tests help, like checking that I'm ovulating?
- Should my partner have a semen analysis?
Your partner in the loop, without an app
Send a private link. They open it in any browser, or subscribe once in Google or Apple Calendar and the dates keep themselves up to date. You choose what they see. Calendar titles are discreet by default, and you can turn the link off in one tap.
- Sun14CycleHelm: plan aheadMar 14 to 19
- Thu1CycleHelm: heads-upApr 1
- Thu8Appointment9:30
Discreet titles are the default. They see dates, never your notes.
Private because it should be
This is health data, and we treat it like it. No ads. No advertising trackers anywhere in the app. Nothing is sold or shared.
- The calculators run on your device. What you type into them is never sent to us.
- We keep only what the features need. Dates, test results, the symptoms you tick and the notes you write. No name, no location, no contacts.
- Stored in the EU. Your account lives on servers in Germany.
- Leave whenever you like. Download everything, or delete it all for good, from Settings. Free, on every plan, immediately.
- Read the privacy policy, written to be read.
Every calculator, free
- Ovulation calculatorYour likely ovulation day and fertile window, with an honest range.Open it
- Due date calculatorFrom your last period, conception, IVF transfer or a scan.Open it
- Fertile window for irregular cyclesWhen your cycles vary, the range that covers them.Open it
- Conception date calculatorWhen conception most likely happened, and the days around it.Open it
- Pregnancy week by weekYour baby's size and what's developing, weeks 4 to 41.Open it
Free for the maths. Pro for someone keeping track.
Pro is $5.99 a month or $39 a year: learned predictions, the weekly pregnancy guide, appointment prep, the clinician summary and partner sharing.
Questions
Is CycleHelm an app I have to download?
No. It runs in your browser on any phone or computer. You can add it to your home screen if you'd like an icon, but there's nothing to install and nothing to update.
How accurate are the dates?
As accurate as the calendar method can be, and honest about it. Every date comes with a range. With a few logged cycles Pro learns how much yours vary, and with ovulation tests it learns your luteal phase, which narrows the range. No calendar method can tell you the exact day you ovulate in a given cycle.
Can I use it to avoid pregnancy?
No. CycleHelm is not birth control and shouldn't be used as it. Calendar estimates miss too often to rely on for that.
Who can see my data?
You. It isn't sold, shared, or used for ads, and there are no ad trackers in the app. If you make a partner link, the person you send it to sees only the dates you chose. You can download everything or delete it all, permanently, any time.
What do I get for free?
Every calculator, an account to log periods, tests, symptoms and notes, this cycle's fertile window and next period, the pregnancy week and baby's size, and full export and delete.
What does Pro add?
Predictions learned from your own history, the full weekly pregnancy guide with a weekly email, appointment prep, a clinician-ready summary and partner sharing. $5.99 a month or $39 a year.