Period Calculator
Estimate your next period from cycle length.
Count from the first day of one period to the first day of the next.
Estimated next period
Introduction
Estimate the start of your next periods from the first day of your last period and your usual cycle length. This is a calendar tool, not a diagnosis, pregnancy test, or contraceptive method.
What is Period Calculator?
Use this tool to make a simple cycle calendar. The cycle length is counted from the first day of one period to the first day of the next. It can be useful for personal tracking, but it cannot diagnose irregular periods, confirm pregnancy, or reliably predict ovulation.
Definition: Period Calculator estimates future period start dates from the first day of the last period and a usual cycle length.
How it works
- Configure the inputs shown in the Period Calculator form above.
- The tool applies the method described by its inputs and result labels.
- Review the result and the assumptions used to produce it.
- Use the related tools below when you need a different pregnancy task.
Worked example
Example: estimate a next period date
Inputs: First day of last period = 1 July 2026, Usual cycle length = 28 days
- Count 28 days from the first day of the last period.
- Display the estimated start of the next period.
- Repeat the same cycle length for the following estimates.
The calculator provides a calendar estimate; cycles can vary from month to month.
Use cases
- Keeping a personal estimate of the next period start date
- Understanding how usual cycle length changes future dates
- Recording a pattern to discuss with a clinician if needed
Advantages
- Browser-based processing — entered values and selected files are not sent to our servers
- No account required
- Instant results with a clean, readable interface
Limitations
- Cycle length can vary naturally from month to month.
- The calculator cannot diagnose irregular periods or explain a missed period.
- It is not a pregnancy test or a contraceptive method.
Frequently asked questions
- What counts as day 1 of a menstrual cycle?
- Day 1 is the first day of your period. A cycle ends on the day before the next period begins.
- What if my periods are irregular?
- A calendar estimate may be inaccurate. Keeping a record can be useful, but talk to a healthcare professional if your usual pattern changes or you are concerned.
- Can this tell me if I am pregnant?
- No. A late or missed period can have different causes. Use an appropriate pregnancy test and seek healthcare guidance when needed.
- Is the Period Calculator free to use?
- Yes. Period Calculator on The Daily Tools is completely free, requires no account, and runs entirely in your browser.
- Does The Daily Tools store my inputs?
- No. Your numbers and text never leave your device. The Daily Tools has no backend database for calculator inputs.
- Who should use the Period Calculator?
- Anyone who needs a clear health and fitness calculation and wants to check the assumptions used.
- How accurate is the Period Calculator?
- Results are computed locally using established methods for pregnancy. Treat outputs as estimates, not professional advice.
- Can I use the Period Calculator on mobile?
- Yes. The Daily Tools is fully responsive and works on phones, tablets, and desktops.
Sources & references
Key points
- Period Calculator is a free, browser-based calculator for estimate your next period from cycle length.
- Estimate your next period from cycle length.
- Private, browser-only processing
- Private, browser-based processing