Cycle maths, done kindly, on your device.
Nineteen free calculators and self-checks for periods, fertility, pregnancy and the patterns worth mentioning to a doctor. No sign-up, nothing saved, nothing sent: close the tab and your answers are gone.
In short: Splash has 19 free period, ovulation, pregnancy and health calculators. They run entirely in your browser, so nothing you type is sent or saved. Each one explains its method, shows results as honest ranges, cites NHS, ACOG or peer-reviewed sources, and says when to see a doctor. None of them is contraception.
Most people start with
When, how long, and is it normal?
Predictions, late-period help and honest checks against the guidelines.
- When is my next period?Your next 6 periods as honest date ranges, plus a calendar file you can keep.Period calculator
- How long is my cycle, and is it regular?Your average cycle, shortest and longest, and whether it's regular, in plain words.Cycle length calculator
- Is my period late?How late you are, what's common, and when testing or a GP makes sense.Late period checker
- Which cycle phase am I in?Which of the four phases you're likely in today, and what's going on in your body.Cycle phase calculator
- Is my period normal?Seven questions, checked against FIGO, ACOG and NHS guidance, with a clear next step.Is my period normal?
- Are my periods too heavy?Eight questions based on NICE and NHS guidance on heavy menstrual bleeding.Heavy period checker
Ovulation, implantation and testing
For trying to conceive or just understanding your cycle. None of these is contraception.
- When might I ovulate?Your estimated ovulation day and fertile window for the next three cycles.Ovulation calculator
- When should I take a pregnancy test?The earliest and the most reliable day to take a home pregnancy test.Pregnancy test timing
- When might implantation happen?When implantation most likely happens, and the first day a test could show it.Implantation calculator
- Did my temperature show ovulation?Paste your morning temperatures to see if, and when, a sustained rise shows up.BBT chart reader
- How is my hCG changing?Doubling time and 48-hour rise between two hCG blood results.hCG calculator
Due dates, weeks and what comes next
From the first test to full term, including IVF dates.
- When is my baby due?Estimate your due date from your last period, conception or IVF transfer.Due date calculator
- When did I conceive?Roughly when conception happened, from your last period or due date.Conception date calculator
- How far along am I?Weeks and days, trimester, month, and what's coming up in your care.How far along am I?
- When is my IVF baby due?Due date and weeks from your embryo transfer (day 3, 5 or 6) or egg collection.IVF due date calculator
- How much weight do people usually gain in pregnancy?The usual range for your pre-pregnancy BMI, week by week, using IOM guidance.Pregnancy weight gain
Spot patterns worth mentioning to a doctor
Short, private self-checks based on the questions clinicians use. They help you decide whether and how soon to see someone; they never diagnose.
- Is it PMS, or could it be PMDD?Eleven symptom areas from the DRSP, plus timing and impact. With support signposts.PMS or PMDD?
- Could I have signs of PCOS?The signs doctors look for, grouped the way the 2023 international guideline does.PCOS signs check
- Could this be perimenopause?The 11 Menopause Rating Scale symptoms, scored by area, with NICE age guidance.Perimenopause symptom check
Why these are different
Your dates never leave the page. The maths runs in your browser. There's no account, no analytics on what you type, and our security policy blocks the page from talking to anyone else.
Ranges, not fake precision. Cycles wobble. We show the likely window around every estimate and say plainly when a guess gets wider.
Honest about limits. None of these tools is contraception or a diagnosis. The health checks use the questions clinicians use (NICE, the DRSP, the Menopause Rating Scale) to help you decide whether and how soon to see someone. Each one tells you when it's worth talking to a GP, and cites the guidelines it uses.
A next step, not a sign-up. Every result ends with what to do next and how to carry it into the Splash app. We never ask for your email.
A calendar file you keep. Period, fertile window, due date and test-day estimates export to Apple, Google or Outlook calendars, with discreet titles if you want them.
Questions about the tools
How do these period, ovulation and due date calculators work?
They apply standard formulas to the dates you enter: the next period is your last start plus your cycle length, ovulation is about 14 days before the next period, and a due date is the first day of your last period plus 280 days (Naegele’s rule). Results are shown as ranges because real cycles vary.
Do the calculators save or send what I type?
No. The maths runs in your browser, nothing you enter is stored or sent to us, and closing the tab clears it. The site sets no cookies and loads no third-party scripts. Calendar files you download are created on your device.
Are the results accurate?
They are estimates, not measurements. A due date is confirmed by your dating scan, and ovulation and period dates move with stress, illness and travel. No tool here is contraception, a medical device or a diagnosis. Each page names the guidelines it follows and when to see a GP.
Which calculator should I start with?
For periods, start with the period calculator. For trying to conceive, use the ovulation calculator, then the pregnancy test timing tool. For pregnancy, the due date calculator. If you are worried about heavy, painful or irregular periods, try the private health checks, which help you decide whether to see a GP.
Sources checked October 2026. More answers in the FAQ.
Want it to learn your cycle?
The Splash app uses the same careful maths, then improves with every period you log. Free to use, no account.