Sade Sati is Saturn crossing the three signs centred on your natal Moon: the one before it, the one holding it, and the one after. Saturn takes roughly two and a half years per sign, so three signs is roughly seven and a half years, which is what the name means.
The calculator above tells you whether it is running for you now, which of the three phases you are in, and when that phase ends. It needs your moon sign, which usually needs only a birth date.
The definition
Find the sign your Moon occupied at birth. That is your chandra rashi, and in Indian practice it is usually what is meant when someone asks your rashi.
Then watch Saturn. When Saturn enters the sign before your moon sign, Sade Sati begins. It continues while Saturn crosses your moon sign itself, and ends when Saturn leaves the sign after it.
Three signs, about two and a half years each. The three stretches are conventionally called the rising phase, the peak, and the setting phase.
Nothing else enters the definition. Not your lagna, not your Sun, not the other planets. It is one transit measured against one natal position, which makes it among the simplest tests in the tradition and one of the easiest to verify.
Why a birth time is usually optional
The Moon holds a sign for about two and a quarter days. So for most birth dates, your moon sign is the same at midnight and at midnight, and the birth time cannot change it.
This page therefore accepts a date alone, and checks. It computes the Moon's sign at the start of your birth day and at the end. If they match, your moon sign is settled and no time is needed. If they differ, it says so and names both, because on that particular day the answer genuinely does depend on the hour.
Roughly one date in ten falls on a lunar sign boundary. On the other nine, asking for a birth time you may not have would be asking for something that cannot affect the answer.
The seven and a half years is approximate, and the dates are not
The name says seven and a half years and most sites treat that as exact, adding thirty months three times to produce the boundaries.
Saturn does not cooperate. Its time in a sign varies because of retrograde loops: it crosses into a sign, turns retrograde, slips back into the previous one, turns direct and re-enters. A sign that takes 27 months on one pass can take 31 on another, and the three phases of any given Sade Sati are not equal.
The phase end date on this page comes from searching for Saturn's actual sign ingress and bisecting to the minute, not from adding a fixed number of months.
That is why it will sometimes disagree with a site that used the arithmetic shortcut, occasionally by several months.
The retrograde behaviour has a second consequence worth knowing. Because Saturn can enter a sign, back out, and re-enter, there is a genuine question about which crossing to date the phase from. This page dates it from the state Saturn is actually in, so a boundary is reported when Saturn is really there. A site dating from first entry will start a phase earlier than one dating from final entry, and both are defensible.
How common is it?
This is the number that puts the rest in proportion.
Saturn takes about 29.5 years to circle the zodiac. It spends about 7.5 of those in the three signs around any given moon sign. So at any moment, roughly a quarter of everyone alive is in Sade Sati.
And because Saturn keeps going, everybody gets it. A person living to seventy-five will pass through Sade Sati two or three times, at intervals of about 29.5 years. If your first was in your teens, expect the next in your forties.
That is a very different kind of claim from a birth-chart feature. Sade Sati is not something your chart has; it is a phase of an external cycle that reaches every moon sign in turn, on a schedule, regardless of anything about you. Being in it now means Saturn is currently in a particular part of the sky, and about one person in four is in the same position.
Dhaiyya, the other one
A related and shorter condition is often mentioned alongside it. Dhaiyya, sometimes called the small panoti, is Saturn transiting the 4th or the 8th sign from your natal Moon.
That is two more signs of the twelve, so about five more years per Saturn cycle. The tool reports it, and reports it as a separate thing rather than folding it in: dhaiyya and Sade Sati cannot both be running, since the 4th and 8th are not among the 12th, 1st and 2nd.
Between them, Sade Sati and dhaiyya cover five signs of twelve. So Saturn is in a marked position relative to your Moon for roughly twelve and a half years out of every twenty-nine and a half, which is about forty per cent of the time. Framed that way, the notable state is arguably the other sixty per cent.
Working out your own timeline
The cycle is regular enough to project by hand, which is useful for sanity-checking anything you are told.
Saturn takes about 29.5 years to return to the same sign. So your Sade Sati periods repeat at that interval. If one began when you were 12, expect the next around 41 or 42, and the one after around 71.
Within a cycle, the structure is fixed: about two and a half years in the sign before your Moon, about two and a half over it, about two and a half in the sign after. Roughly seven and a half in total, though as described above the phases are not equal in practice.
That regularity has a consequence worth stating. Sade Sati is entirely predictable decades in advance, because it depends on nothing but Saturn's orbital period and your moon sign, both of which are known. Nobody needs to compute anything special to tell you when yours falls; the dates were determined the moment your moon sign was.
It also means the periods are shared. Everyone with your moon sign, anywhere in the world, of any age, is in Sade Sati at exactly the same times you are. The cycle is a property of Saturn's orbit, not of a person.
The dhaiyya arithmetic
Adding the two conditions together gives a figure worth keeping in mind.
Sade Sati covers three signs of twelve. Dhaiyya covers two more. Five signs of twelve is about 42% of Saturn's circuit, so Saturn is in a marked position relative to your Moon for around twelve and a half years out of every twenty-nine and a half.
Over a lifetime of seventy-five years, that is roughly thirty-one years spent in one or other of these states. Almost a third of a life.
That is not an argument that the tradition is wrong about anything. It is a note about what the categories can do. A label applied to a third of everyone's life, on a fixed schedule that nobody can alter and everyone shares, is not distinguishing your circumstances from anyone else's. If a difficult period coincides with Sade Sati, so does about a third of every period, difficult or not.
Why another site gives you different dates
The ayanamsa, and this one matters more than usual. Everything here depends on the natal moon SIGN, which is an absolute position. Lahiri and Raman sit about 1.45° apart, so a Moon within that distance of a sign boundary gets a different sign under the two systems, and a different sign means an entirely different Sade Sati timeline, shifted by about two and a half years. The selector above lets you check whether your Moon is close enough to a boundary for this to bite.
Adding thirty months versus finding the ingress, as described above. Worth up to several months at each boundary.
First entry against final entry into a sign, when Saturn retrogrades back out and returns. Also worth months.
The birth time on a boundary date, for the one date in ten where the Moon changed sign.
Note what is not on that list: the birth place and the birth time in general. Sade Sati depends on the Moon's sign and Saturn's sign, both of which are geocentric positions independent of where on Earth you were. This is one of the few readings on this site that is genuinely insensitive to a rough birth time.
Reading a Sade Sati result
Three things to establish before anything else.
Is your moon sign settled? If your birth date is one where the Moon changed sign, everything downstream is provisional until a birth time is found.
Is the Moon near a sign boundary? If it is within about 1.5°, different ayanamsas will disagree about your sign, and therefore about your dates.
Which phase, and how far into it? The three phases are not equal lengths, so "halfway through Sade Sati" is not the same as "eighteen months into the middle phase". The tool gives the actual end date of the phase you are in.
What this page will not do
It will not tell you that the next seven and a half years will be difficult.
Sade Sati carries a heavy reputation, and a substantial industry exists around mitigating it. What this page computes is where Saturn is, where your Moon was, how many signs apart those are, and when Saturn next crosses a sign boundary. Each of those is a position or a date checkable against any ephemeris.
The one thing worth carrying away is the base rate, because it reframes the finding without disputing it. A quarter of the world is in Sade Sati right now. Everyone you know has been through it or will be, two or three times, on a fixed schedule set by Saturn's orbital period and nothing else. Whatever significance the tradition assigns to that, it is not a statement about you in particular, and it was never going to skip anybody.