Astrology
Every Astrology tool on Toolz.dev: 14 free utilities that run entirely in your browser. No signup, no uploads, no downloads.
An astrology calculator works out where the Sun, Moon and planets stood at the moment you were born, and translates those positions into the vocabulary a reading uses: signs, houses and aspects. Everything in this category starts from the same three facts - a date, a time and a place - and differs only in which part of the resulting chart it answers. The full birth chart shows all of it at once; the single-placement calculators answer one question each, which is usually the faster way in.
The three placements people ask for first are the Sun, the Moon and the ascendant, together called the big three. Your Sun sign is the one you already know from a birthday. Your moon sign needs a birth time on about two days in five, because the Moon crosses a whole sign every two and a half days. Your rising sign needs an exact time and a place without exception - the entire zodiac passes over the eastern horizon every twenty-four hours, so it changes roughly every two hours. If you want all three in one pass, use the sun, moon and rising sign calculator. Where the question is about the months ahead rather than the chart itself, the dating and growth calendar scans transits day by day and marks the ones worth knowing about.
Which astrology calculator to use, and what each one needs
| Calculator | What it needs | What it tells you |
|---|---|---|
| Sun sign | Birth date | Core identity and sense of purpose |
| Moon sign | Date; time on cusp days | Emotional nature and what makes you feel safe |
| Rising sign | Exact time and place | First impressions and how you approach anything new |
| Sun, Moon and rising | Date; time and place for all three | The big three in one pass, with how they interact |
| Birth chart | Exact time and place | Ten bodies, twelve houses and every aspect |
| Venus sign | Birth date | How you love and what you find beautiful |
| Chiron sign | Birth date | The early wound, and what you can help others with |
| Black Moon Lilith | Birth date | What you were taught to suppress |
| North Node | Birth date | The direction of growth, with the South Node opposite |
| Part of Fortune | Exact time and place | Where ease and flourishing are said to be found |
| Vertex | Exact time and place | Fated encounters and turning points |
| Synastry | Both charts, with times | Every aspect between two people, in both directions |
| Love compatibility | Both dates; times help | A score, with the contacts that produced it |
| Dating and growth calendar | Date; time and place help | Which days ahead carry supportive or difficult transits |
What a birth chart is made of
Three layers sit in every chart, and confusing them is the usual source of a reading that does not land. The signs describe the character a placement takes: Mars in Libra pursues differently from Mars in Aries. The houses describe the area of life it plays out in, and they depend entirely on the birth time, since the whole zodiac crosses the horizon each day. The aspects describe how the placements relate to one another - a square between two planets is read as friction, a trine as ease. A single-placement calculator gives you the first layer; the birth chart gives you all three.
Beyond the ten bodies, a chart carries calculated points that are geometry rather than objects. Black Moon Lilith is the apogee of the Moon's orbit. The lunar nodes are where that orbit crosses the ecliptic, which is also why eclipses only happen near them. The Part of Fortune is the ascendant carried the arc between the Sun and Moon, and the vertex is where the ecliptic meets the circle running from due east through the zenith to due west. None of them is a body; all of them have a long reading tradition.
Why two calculators disagree
Almost every disagreement between astrology sites is a convention, not an error, and there are four common ones. A different house system moves every house cusp without moving a single planet. Different aspect orbs decide whether a contact exists at all. A time zone rule applied from today rather than from your birth date is an hour out, which is about half a sign of ascendant. And the lunar node comes in a mean and a true version that differ by up to 1.6 degrees.
The tools here state which convention they used, next to the answer, so a difference can be traced instead of argued about. Where a choice genuinely changes the result - a birth on the night a clock went back, a placement sitting on a cusp, an unknown birth time - the tool says so and shows both possibilities rather than quietly picking one.
How the positions are calculated
Every position here is computed from an astronomical model rather than looked up in a table of date ranges. The solar and lunar positions come from the standard series in Jean Meeus's Astronomical Algorithms, the planets from the VSOP87 planetary theory, and Chiron and Pluto from sampled ephemerides published by JPL. Each one is checked against JPL Horizons - NASA's own ephemeris service - at dates spread across two centuries, and the largest disagreement for any body is under fourteen arcseconds, roughly a two-thousandth of the width of a zodiac sign.
That matters most where a table gets it wrong. Fixed date ranges cannot handle a cusp birthday, because the Sun enters each sign at a slightly different moment every year. They cannot handle a planet going retrograde back across a boundary it already crossed. And they cannot say how close to a boundary a placement actually sits, which is the only way to know whether a remembered birth time is precise enough to trust. Everything runs in your browser: the birth details you enter are never uploaded, logged or stored.
Frequently asked questions
- What do I need to calculate my birth chart?
- A birth date, a birth time and a birth place. The date fixes the planets, the time fixes the houses and the angles, and the place fixes the horizon and the time zone your local birth time has to be converted from. Without a time you can still see every planet's sign, but not the ascendant, the midheaven or any house.
- Which astrology calculator should I start with?
- The sun, moon and rising sign calculator, if you have a birth time - the big three are the shorthand version of a chart and describe most of what people recognise in themselves. Without a time, start with the Sun and Venus, which the date alone settles on nearly every birthday.
- Do I need my exact birth time?
- For the ascendant, the midheaven, the houses, the vertex and the Part of Fortune, yes - all of them move a full circle through the zodiac every day. For the Moon it matters on about two days in five. For the Sun, Venus, Chiron, Lilith and the nodes the date is almost always enough, and each tool says when it is not.
- Do these tools use tropical or sidereal astrology?
- Tropical, which is what Western astrology uses. It measures from the vernal equinox, so zero degrees Aries is the equinox point. Vedic astrology uses the sidereal zodiac, measured against the fixed stars, which precession has moved about twenty-four degrees away from the tropical one - which is why a Vedic chart usually reports the sign before the one you know.
- How accurate are these calculations?
- Every body is verified against JPL Horizons across 1900 to 2100, with the largest error under fourteen arcseconds. In practice the arithmetic is never the limit - a birth time recorded to the nearest five minutes already moves the ascendant by more than a degree, which is far larger than any error in the astronomy.
- Is my birth information stored anywhere?
- No. Every calculation runs in your browser in JavaScript, and the city list is a static file downloaded to your device. Nothing you type is sent to a server, written to a database or associated with you, and the pages keep working with the network disconnected.