What this page is
And, more importantly, what it is not.
This explains the subject the app is built around: what niddah means, what the stages of the cycle are called, how the dates on your calendar are worked out, and where each rule is written. It is here so that nothing on your calendar is a number you cannot account for.
Nothing here is a psak.
This is a description of a body of halacha and of a piece of software, written so that you can follow both. It cannot rule on your situation, because a ruling depends on facts a page cannot see. Every real question — a colour, a date you are unsure of, a stain, anything that does not fit the pattern — goes to your Rav.
Practice differs between communities on a number of the points below. Where it does, this page says so and names which practice the app follows, rather than presenting one as though it were the only one.
What niddah means
The state itself, before any counting.
A woman who experiences uterine bleeding enters a halachic state called niddah. It is a status, not a description of health: it begins when she sees, and it ends only after a count is completed and she immerses in a mikvah. While it lasts, physical relations between husband and wife are forbidden.
The word itself refers to the separation. The couple keep a set of practices during this time, collectively called harchakos, which go beyond relations themselves. What they consist of, and how they are kept in practice, is a subject of its own.
What makes a woman a niddah
Not everything red is blood, and not all blood renders a woman temei’ah. Colour, source and circumstance all matter, and the distinctions are fine ones. This is why the app never asks you what colour anything was and never draws a conclusion from one — a cloth in question goes to a Rav, not to software.
The cycle from beginning to end
Five stages. Everything else on this page is detail inside one of them.
- The period begins. She sees, and becomes a niddah. The app records the date and whether it was before or after shkiah.
- The bleeding stops. A minimum number of days is waited from the onset before the next step — 5 in the practice this app follows.
- The hefsek taharah. An examination before shkiah that establishes the bleeding has stopped, and opens the count.
- The seven clean days. 7 days of counting, with bedikos, beginning the day after a valid hefsek.
- Mikvah night. The night following the seventh clean day. Immersion ends the state.
Alongside that count runs a second, independent one: anticipating when the NEXT period is likely to come, so that the couple separates in advance. Those expected times are the onos, and they are the other half of what your calendar shows.
When one day becomes the next
Shkiah, and why an evening belongs to tomorrow.
A Jewish day runs from sunset to sunset. Something seen after shkiah belongs to the following Jewish day, not the one whose daylight has just ended. This single fact is behind most of the confusion people have with these calculations, and it is why the app asks "before or after shkiah?" every time you record something.
- Onah
- Half a Jewish day. The night onah runs from shkiah until dawn; the day onah runs from dawn until shkiah. Times of expectation are reckoned in onos, not in whole days.
- Shkiah
- Sunset, as calculated for your location. Set your city in Settings and the app uses your own times; without it, the times shown are not yours. Communities also differ on which calculation of shkiah to follow — check the time against your usual luach.
How the app stores this
Your onset date is stored as the JEWISH day it belongs to. If you saw on Tuesday evening after shkiah, the app records Wednesday and remembers that it was the night onah. That is why a date you enter can appear as the following day, and it is correct.
The days of the period
From when she sees until the hefsek may be done.
The first stage lasts as long as the bleeding does, with a minimum. Ashkenazi practice waits five days from the onset before the hefsek taharah, counting the day she saw as day one — so the hefsek is done on day five at the earliest. Sephardi practice on this differs, and there are circumstances in which a Rav rules otherwise.
Day five is a floor, not a deadline
The app prompts you from day five onwards because that is the earliest the hefsek may be done. If the bleeding has not stopped, it has not stopped; the prompt returns the next day and nothing is wrong.
The hefsek taharah
The examination that closes the period and opens the count.
The hefsek taharah is an internal examination with a clean white cloth, performed before shkiah, which establishes that the bleeding has stopped. It is the hinge of the whole cycle: the seven clean days begin the following day, and without a valid hefsek there is nothing to count from.
- It must be done before shkiah. One done after shkiah does not open the count.
- The seven clean days begin on the day AFTER the hefsek, not the same day.
- If what the cloth shows is in question, that is a sheilah — the cloth itself is what a Rav looks at.
What the app does with a late hefsek
If you record a hefsek after shkiah, the app saves it but does NOT build seven clean days or a mikvah night from it, and flags it. It would rather show you nothing than show you a mikvah night that rests on an invalid hefsek.
Related practices — the moch dachuk, and an examination in the days before the hefsek — vary by community and by circumstance, and are not modelled by the app at all.
The seven clean days
Where the counting actually happens.
Seven consecutive days are counted, beginning the day after a valid hefsek taharah. On each of them two bedikos are performed, one in the morning and one towards evening before shkiah. The count must run clean from beginning to end; anything seen during it voids what has been counted so far.
Why seven, for every period
In Torah law seven clean days belong to a zavah, not to an ordinary niddah. Bnos Yisrael accepted upon themselves to count seven clean days even for a single drop, and that acceptance is binding practice — which is why every period today is followed by the same count.
The first and the seventh day carry particular weight in the bedikos. The app marks those two days when a bedikah on them has not been recorded, and attaches a warning to the calculated mikvah night rather than letting it stand unqualified.
A bedikah not logged is not a bedikah missed
The app never assumes either way. It asks you which it was, and a genuine miss stays in your record permanently, so that you can raise it rather than discover later that it was quietly dropped.
Mikvah night
What ends the state.
Immersion takes place on the night following the seventh clean day, after nightfall — not earlier in that day. Counting alone does not end the state of niddah; the immersion does.
Preparation (chafifah) precedes it and needs real time, so it is begun well before shkiah. Anything interposing between the body and the water (chatzitzah) invalidates the immersion, which is what the preparation is for.
What counts as a valid mikvah is a subject in its own right, and is not something a user of this app decides — it is a property of the mikvah itself.
Postponing
A mikvah night that cannot be kept is postponed, not skipped, and the state continues until immersion. The app lets you move the date and keeps the cycle open until you confirm you went — an unconfirmed mikvah night is the one thing it keeps asking about.
Vesatos — anticipating the next period
The second count, and the one people find hardest.
A woman is obliged to anticipate when her next period is likely to arrive, and the couple separates at that expected time. The expected times are worked out from her own history, which is the reason a record of dates is worth keeping at all.
A woman whose periods do not follow a fixed pattern — the majority — anticipates three separate times after each period. The app draws all three.
| Onah | When it falls | Counted from |
|---|---|---|
| Ona Beinonis, day 30 | The thirtieth day from the onset | The day she saw counts as day one |
| Day 31 | The day after | Observed alongside day 30 in many communities |
| Yom HaChodesh | The same Hebrew day of the following month | The Hebrew date of the onset |
| Haflaga | The interval between her last two periods, projected forward | See below — the counting method differs by community |
Which half of the day is observed — the onah she actually saw in, or both the day and the night — is a genuine dispute. This app marks BOTH onah, which is the stringent side. If your Rav holds otherwise, the calendar is showing you more than you need.
Haflaga is counted differently in different communities
This app counts the haflaga in DAYS from one onset to the next, counting the day she saw as day one — Satmar and Hungarian practice. Chabad counts it in ONOS from the hefsek taharah to the next flow, which produces a different number from the same history. Both are right, for different people. If you follow the second, the haflaga dates this app shows you are not yours.
Veset kavuah — an established pattern
When the pattern is fixed, the rules change.
If periods arrive in a consistent pattern often enough, that pattern becomes an established veset — a veset kavuah — and it displaces the general anticipations above. Three consecutive occurrences in the same pattern, in the same onah, are what establish one.
An established veset is uprooted when the expected time passes without a period three consecutive times. Until then it stands.
The app checks your full history for these patterns automatically and shows you what it found and on which sightings. It reports a candidate; whether you HAVE an established veset, and what follows from it, is a determination for your Rav.
One kind it cannot detect
A veset ha-guf is established by a recurring physical sensation rather than by a date. The app does not record symptoms, so it cannot see one, and it will not tell you that you have no veset when you may well have one it cannot look for.
Stains
A stain found is not the same as a flow felt.
A kesem is a stain discovered on a garment or a cloth, as distinct from bleeding she felt. The rules governing it are different and are highly detailed: the size of the stain, what it was found on, and its colour all bear on the outcome. A stain smaller than a gris on a surface that is not susceptible to tumah may not render her temei’ah at all.
This is not a determination the app makes, and it is not one to make from a page either. Record what you saw while the details are fresh — colour, size, which cloth, which day of the count — and bring it. The Questions for a Rav panel exists for exactly this.
Why the app asks "flow or stain?"
A stain during the seven clean days voids the count — a new hefsek is needed — but it does NOT move your onos, because vesatos are reckoned from an actual sighting. A real flow does both: it voids the count AND re-anchors day 30, Yom HaChodesh and the haflaga. The two answers lead to different calendars, which is why the app will not guess between them.
When the count is interrupted
What the app does, and what it deliberately does not do.
| What happened | The count | Your onos |
|---|---|---|
| A real flow during the seven clean days | Void — hefsek and mikvah night are cleared | Re-anchored to the new date |
| A stain during the seven clean days | Void — a new hefsek is needed | Unchanged |
| A hefsek recorded after shkiah | Not opened | Unchanged |
| A bedikah missed on day 1 or day 7 | Kept, with a warning on the mikvah night | Unchanged |
In each of these the app changes what it draws, and says why. It does not decide the underlying question. Where a case turns on something it cannot see — what the cloth looked like, what you felt — it flags the entry rather than resolving it.
Bringing a question to a Rav
What to record, and what he will ask.
Most questions in this area turn on details that are easy to lose within a day. Writing them down at the time is the single most useful thing you can do, and it is what the Questions for a Rav panel is for.
- When it happened — the date, and whether before or after shkiah.
- What you saw — colour, size, and how certain you are of both.
- Where you saw it — a bedikah cloth, underwear, a coloured garment.
- Where you were in the count — day of the period, or which of the seven clean days.
- Whether it was felt or only found.
The app can prepare the question for you
From the Questions panel you can email a question to your Rav — set his address in Settings first — or print it as a sheet. Either way it goes out with the dates from your record that bear on it, so you are not reconstructing them from memory in front of him.
Record what he answers, too. A ruling that you were not tahor means the dates already on your calendar are wrong, and the app will offer to correct them rather than carrying on with a count that no longer holds.
What this app does not know
Stated plainly, because the gaps matter more than the features.
- Colours. It never asks and never judges. Every colour question is a sheilah.
- Pregnancy, nursing and menopause. The veset rules change substantially in each, and the app has no concept of them — it will keep projecting a day-30 onah straight through a pregnancy.
- Veset ha-guf, and any pattern based on physical symptoms rather than dates.
- Your community’s practice, beyond the specific positions listed in Settings.
- Whether the mikvah you use is valid, or anything else about the immersion itself.
- Any circumstance you have not recorded. It calculates from what it was told and nothing else.
The positions the app takes have not been reviewed by a Rav
A number of the choices behind these calculations are still open questions, and they are all listed in Settings with what was chosen and what the alternative was. Show that list to your Rav. Until he has been through it, treat the dates here as a record of your own data rather than as guidance.
Glossary
The terms as they are used in the app.
- Niddah
- The status a woman enters on seeing uterine blood, and the separation that accompanies it.
- Onah
- Half a Jewish day — night (shkiah to dawn) or day (dawn to shkiah).
- Shkiah
- Sunset. The boundary between one Jewish day and the next.
- Ra’iyah
- A sighting of an actual flow, as opposed to a stain found afterwards.
- Kesem
- A stain found on a cloth or garment. Governed by its own detailed rules.
- Gris
- A measure of size used in the laws of stains; below it, a stain may not render her temei’ah.
- Hefsek taharah
- The examination before shkiah establishing that bleeding has stopped, which opens the count.
- Bedikah
- An internal examination with a white cloth. Two are done on each of the seven clean days.
- Moch dachuk
- A cloth left in place for a period after the hefsek. Practice on it varies.
- Shivah neki’im
- The seven clean days, counted from the day after a valid hefsek.
- Tevilah
- Immersion in a mikvah, on the night following the seventh clean day.
- Chafifah
- The preparation preceding immersion.
- Chatzitzah
- Anything interposing between body and water, which invalidates the immersion.
- Veset
- An expected time for the next period.
- Veset kavuah
- An established pattern — three consecutive occurrences in the same pattern and onah.
- Ona beinonis
- The thirtieth day from the onset, counting the day she saw as day one.
- Yom HaChodesh
- The same Hebrew day of the following month as the onset.
- Haflaga
- The interval between two consecutive onsets, projected forward to the next.
- Harchakos
- The practices kept between husband and wife while she is a niddah.
- Sheilah
- A question brought to a Rav.
Every source cited
The full list, with what this app cites each one for. Citations marked siman only name the siman but do not claim a particular se’if — check those in your own sefer before relying on the reference.
Torah
A woman who sees blood becomes temei’ah. This is the state the whole subject is about.
A zavah counts seven clean days once the flow has stopped — the origin of the seven-day count.
The prohibition itself, which is why these dates matter rather than being a health record.
Immersion in water is what ends the state. Counting alone does not.
Talmud
Bnos Yisrael accepted upon themselves to count seven clean days even for a drop the size of a mustard seed. This is why every period, and not only a zavah, is followed by seven clean days.
- Niddah 63bsiman only
The sugya of vesatos — that a woman is obliged to anticipate her expected time.
Rambam
- Rambam, Hilchos Issurei Biah 8siman only
The laws of vesatos set out in order — kavuah and she’eino kavuah.
Records the accepted custom of seven clean days as binding practice.
Shulchan Aruch
- Shulchan Aruch YD 183siman only
The opening siman of hilchos niddah — how a woman becomes temei’ah.
A couple separates at the onah when a period is expected.
Which onah is observed — the day or the night. This is the source behind the app’s choice to mark both, which is the stringent side of the question.
- Shulchan Aruch YD 186siman only
Bedikos before and after, and when they are required.
- Shulchan Aruch YD 188siman only
Which colours render a woman temei’ah. The app never judges a colour; this is the siman that explains why that is a question for a Rav and not for software.
- Shulchan Aruch YD 189siman only
Vesatos in full — how a veset kavuah is established, and how one is uprooted.
A woman with no established veset anticipates the thirtieth day, the same day of the Hebrew month, and the haflaga. These are the three onos the app draws.
- Shulchan Aruch YD 190siman only
Kesamim — a stain found, as distinct from a flow felt. A long and detailed siman.
A stain smaller than a gris does not render her temei’ah — so size is one of the things a Rav will ask about.
- Shulchan Aruch YD 195siman only
The harchakos kept while she is a niddah.
- Shulchan Aruch YD 196siman only
The hefsek taharah and the seven clean days, including the bedikos kept during them.
The hefsek taharah is done before shkiah; the seven clean days begin the following day.
Ashkenazi practice waits five days from the onset before the hefsek taharah. This is why the app does not offer a hefsek before day five.
- Shulchan Aruch YD 197siman only
When the tevilah takes place — the night following the seventh clean day, and not before nightfall.
- Shulchan Aruch YD 198siman only
Chatzitzah, and the preparation (chafifah) that precedes immersion.
- Shulchan Aruch YD 201siman only
The mikvah itself — what makes one valid.
Community practice
- Satmar / Hungarian practicesiman onlyno online text
The haflaga is counted in DAYS from one onset to the next, counting the day she saw as day one. This app follows it. That is a choice of whose practice to encode, not a ruling.
- Shulchan Aruch HaRav (Chabad practice)siman onlyno online text
Counts the haflaga in ONOS from the hefsek taharah to the next flow, which gives a different number for the same history. This app does NOT follow it.
Links go to Sefaria, which hosts the texts in Hebrew with English translation. The app has no affiliation with Sefaria and does not control what is shown there.