About AstroCalcs
Astrology calculators that take the astronomy seriously: the dates come from a real ephemeris, to the minute, and nothing you type leaves your browser.
To the minute
Positions come from astronomy-engine, and each tool searches for the exact instant an event happens instead of rounding to a month.
In your browser
Every calculation runs on your device. Your birth details are never uploaded, saved or tied to an account.
No paywall
Nothing to sign up for and no chart held back for a fee. Ads cover the domain.
Shows its working
Each tool states what it assumes and where the birth time changes the answer, with a methodology page to check it against.
What AstroCalcs is
AstroCalcs is a small set of astrology calculators that compute each result from the actual positions of the Sun, Moon and planets. Each tool runs a real ephemeris and searches it for the moment something happens: the instant Saturn gets back to its natal degree, the minute the Sun returns to where it was when you were born, the degree that was rising over the horizon at that moment. You get the date and time first. What astrologers say it means comes after, and is labelled as such.
It is free and it runs in your browser. There is no account to create and no chart held back behind a paywall, and no server sees the details you type. The site carries ads, which pay for the domain. Under the hood it is a set of static pages with a few small interactive islands, so it loads fast and behaves the same whether you visit once or come back every Mercury retrograde.
Who it's for
People who are curious. If you have heard your Saturn return is coming and want dates rather than a shrug and "late twenties", this is for you. If you are learning astrology and want a tool that shows its working instead of a black box, it is for you too. And if you are the friend who always knows when Mercury is retrograde, you can now quote the station to the minute.
I assume no prior knowledge. Each calculator asks only for what it needs, usually a birth date, sometimes an exact time and place, and every result explains the astronomy and the astrology in ordinary words. You do not need to know what an ecliptic longitude is to use the rising sign calculator. You need your birth details and about a minute.
Why I built it
Every free astrology calculator I tried fell into one of two camps: a pretty page that quietly rounded everything to the nearest month, or accurate software that wanted an account first and treated my birth data as the product. Neither seemed right. Where and when you were born is about as personal as data gets, so I made the site compute everything in your browser, where nothing you type is transmitted or stored, and I made it precise enough that the dates hold up.
The other reason was the licence. astronomy-engine, the ephemeris library underneath, is MIT-licensed and open source, which means the site can run it in your browser for nothing and stay free. I also wanted to be plain about the limits. A Saturn return is reliable from a birth date alone. An ascendant can swing by a whole sign if the birth time is an hour out. Each tool says which kind it is, and the methodology page lays out how the numbers are produced and tested.
How the numbers are made
Positions come from the MIT-licensed astronomy-engine, and what the site reports is apparent geocentric ecliptic longitude in the tropical zodiac. Your local birth time becomes an exact instant through the IANA time zone database, using the offset and daylight-saving rule that applied on your birth date rather than today's. The coordinate frame, the accuracy checks against JPL reference data and the caveats for each tool are all on the methodology page.
The ten calculators
Each one searches a real ephemeris and then explains the result. Pick one.
Big 3
Sun, Moon and rising sign together, each to the exact degree, from your birth details.
Saturn Return
The dates of your first, second and third Saturn returns, retrograde passes included.
Solar Return
The minute the Sun gets back to its natal degree each year, in the time zone you choose.
Rising Sign
Your ascendant and big three from an exact birth time and place. No time, no guess.
Black Moon Lilith
Your Mean Black Moon Lilith by sign, exact degree and house.
Birth Moon Phase
The Moon's phase and sign at the moment you were born, and what astrologers say that pairing means.
Moon Phase Compatibility
Two birth Moon phases compared, for how your emotional rhythms fit or grate.
Natal Retrograde
Which of the 8 planets were retrograde when you were born, from the date alone, and how common each one is.
Mercury Retrograde
Station dates for every Mercury retrograde and shadow period, searched from the ephemeris to the minute.
Cycle Lab
Every eclipse and planetary station near any zodiac degree, 1900–2100, beside the baseline that says whether it means anything.
Reference tables
Beside the calculators there are twenty lookup pages from the same ephemeris. Nothing to enter; they are just the dates.
Questions about AstroCalcs
The short answers, for anyone who scrolled here first.
Who makes AstroCalcs?
One person, who likes the sky a little more than the horoscope column and got tired of calculators that round to the month. There is no team behind it, and no name on it: the methodology page is a better credential than a bio would be.
Is AstroCalcs really free?
Yes. There is nothing to sign up for and no paywall with a chart behind it. The maths runs in your browser, so there is no server doing work I would need to charge you for. The site carries ads, which is how it pays for its domain.
Do you store my birth details?
No. The calculations happen on your device, so your birth date, time and place never leave your browser. There is no account and no database of charts, which also means there is nothing to leak. The privacy page spells it out.
Are you professional astrologers?
That is a question about credentials, and the site is easier to judge by what it shows. The astronomy is tested against JPL reference data. The astrology is the standard material, framed as what astrologers say. The interpretations describe what people with a placement tend to report and do not predict anything, and nothing here is medical, financial or legal advice.