Project upcoming period start and end dates.
How to use this calculator
Every field updates the result as you type — there is no submit step. The inputs below are pre-filled with a realistic example so you can see how the tool behaves before entering your own figures.
| Field | Unit | What it means |
|---|---|---|
| First day of last period | date | Pick a date from the calendar. |
| Cycle length | days | Enter a numeric value. |
| Period duration | days | Enter a numeric value. |
| Cycles to project | — | Enter a numeric value. |
Worked example
Using the default values loaded into the calculator above, the result is:
| Input | Value |
|---|---|
| First day of last period | 2026-07-23 |
| Cycle length (days) | 28 |
| Period duration (days) | 5 |
| Cycles to project | 12 |
| Output | Value |
|---|---|
| Next period starts | Thursday, August 20, 2026 |
| Ends approximately | Monday, August 24, 2026 |
| Days until next period | 27 |
Reading the result
Health calculators apply population-level equations to an individual. They are screening and planning aids, useful for tracking direction over time, but they cannot account for your medical history, medication or body composition.
This is general information, not medical advice. Discuss anything that concerns you with a qualified clinician.
Sharing and saving a calculation
The "Copy link" button encodes every value you have entered into the page URL. Opening that link restores the calculation exactly, which makes it easy to bookmark a scenario, send it to someone else, or keep several variations side by side in separate tabs.
Frequently asked questions
What does the Period Calculator do?
Project upcoming period start and end dates.
What result do the default values produce?
With the values pre-loaded in the calculator, next period starts comes to Thursday, August 20, 2026.
Is this calculator free to use?
Yes. It is free, requires no account, and runs entirely in your browser — nothing you enter is transmitted or stored on a server.
Can I save or share a calculation?
Yes. The "Copy link" button builds a URL containing all your entered values. Anyone opening that link sees the same calculation.
How accurate is the result?
The calculation itself is exact for the inputs given. Real-world accuracy depends on how well those inputs reflect your actual situation, so review the assumptions before relying on the figure.