Free Tropical vs Sidereal Chart Calculator
Tropical and sidereal astrology can put you in a different sign for the same birth data, because the two zodiacs are built from different reference points that have drifted apart over the centuries. This calculator runs your chart through both frames at once and shows you, planet by planet, which of your placements actually change sign and which don't.How it works ↓
Calculating your placements…
The tropical zodiac lines signs up with the seasons; the sidereal zodiac lines them up with the actual background of stars, and the gap between the two has been widening for two thousand years. This calculator casts your chart in both zodiacs side by side, so you can see exactly which placements shift into a different sign and which stay put.
What separates the tropical and sidereal zodiacs
The tropical zodiac is anchored to the seasons: 0 degrees Aries is defined as the spring equinox, the moment the Sun crosses the celestial equator each year, regardless of which constellation happens to be behind it. This is the zodiac most Western astrology, including the sign you probably already know, is built on.
The sidereal zodiac is anchored to the stars instead, keeping 0 degrees Aries fixed against a background constellation rather than the equinox. Vedic astrology uses the sidereal zodiac, most commonly with the Lahiri ayanamsa as its reference point. The two zodiacs are not two opinions about the same thing; they are two different rulers laid over the same sky.
Why the gap keeps growing
Earth wobbles slowly on its axis, a motion called the precession of the equinoxes, completing one full wobble roughly every 26,000 years. The tropical zodiac ignores this wobble by design, staying locked to the equinox every year. The sidereal zodiac does not, so as Earth's axis slowly traces its circle, the two reference points drift further apart.
They were roughly aligned around two thousand years ago and have been separating since, at a rate of about one degree every 72 years. Today the offset, called the ayanamsa, sits at roughly 24 degrees: nearly a full zodiac sign's width.
How to read your comparison
The "where they disagree" table shows every planet that landed in a different sign between the two zodiacs for your chart. A planet only crosses into a new sign if it sat within about 24 degrees of a sign boundary in the tropical chart, since that is roughly the size of the current offset.
Because 24 degrees is most of a 30-degree sign, a lot of placements do move, more often than with house systems. But planets that sit deep in the middle of a tropical sign, more than 24 degrees from either edge, land in the equivalent sidereal sign every time. Where your chart falls on that spectrum is exactly what the comparison shows.
Which traditions use which zodiac
Tropical is the standard in Western astrology: sun-sign columns, most modern software defaults, and the astrology most people in Europe and the Americas grew up with all use it. Sidereal is the standard in Vedic, or Jyotish, astrology, which developed its own house and dasha techniques around the star-based frame.
Neither tradition treats the other's zodiac as a rival system to disprove; they are simply built on different foundational choices, each internally consistent within its own practice.
Does this mean one of your charts is wrong?
No. Tropical and sidereal are two different, self-consistent reference frames for measuring the same physical sky, not competing claims about where your planets actually are. Every planet's real position is identical in both charts; only the zodiac used to label that position changes.
Whether one frame interprets you more accurately is a question of which tradition's methods you find useful, not an astronomical dispute this calculator can settle either way.
When the shift matters most
If several of your placements sit within a few degrees of a sign boundary in your tropical chart, expect real differences in the sidereal comparison, since the roughly 24-degree offset is enough to carry a borderline placement across. If your placements sit comfortably mid-sign, expect the sidereal chart to mostly restate the tropical one, just in a different named sign further back in the zodiac.
If you already work in the sidereal frame day to day, whether through Vedic practice or a preferred ayanamsa, the dedicated sidereal chart and Vedic Kundli calculators linked below give you that single frame without the comparison layer.
Frequently Asked Questions
Why do tropical and sidereal give different signs?
The two zodiacs are offset by the ayanamsa, an angle of roughly 24 degrees today caused by the slow precession of the equinoxes since the tropical zodiac's reference point was fixed. That is often enough to shift a planet into the sign next door.
Which zodiac is more accurate?
Neither. Tropical and sidereal measure the same real planetary positions using two different reference points, one anchored to the seasons and one to the stars, so the disagreement is about which frame to use, not which one got the physics wrong.
Why didn't any of my placements change sign?
A planet only crosses into a different sign when it sits within about 24 degrees of a sign boundary in the tropical chart, close to the current ayanamsa offset. Placements comfortably in the middle of a sign land in the matching sidereal sign every time, which is a genuine result, not a missed comparison.