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Calculation Tools for AI Astrology

A comparison of four free tools to calculate astrological data for AI interpretation: Astro.com, Astro-Seek, Astro-engine.com, and AstroPrompt.

I've made the point on other pages of this website: AI astrology gives great interpretations, but DON'T ask ChatGPT or any other LLM to calculate a birthchart.

For accurate astrological interpretations from AI, you MUST use a website or software tool that does astronomical math, which an AI can't do. Get accurate astrological data, and you can great readings from any AI chat.

Here I compare four tools that will give you accurate astrological data. These are the four tools I reach for when I need accurate chart data ready for an AI chat: Astro.com (the long-standing professional standard), Astro-Seek (a firehose of calculation tools), Astro-engine.com (a new freemium service with integrated Claude AI), and AstroPrompt (the workbench I built for AI astrology).

All four use the Swiss Ephemeris under the hood, so the underlying math is equally good across them. The differences are in everything else: how you interact with the tool, whether it integrates AI, what it costs, your privacy, and whether you can edit the prompt that starts the AI chat.

For an overview of the broader AI-astrology workflow, see the Astrology Prompts for AI article. To compare ChatGPT, Claude, and other LLMs, see Best AI for Astrology.

Before you get started

If you just want a recommendation, I'll suggest the tool I built, AstroPrompt. It calculates the chart and combines the data with a prompt ready for a ChatGPT or any AI chat. Try AstroPrompt now; it is FREE and gives you calculation confidence with any AI chat.

Leading Free Products

Here's a one-line summary of each tool. They are all good but I'll explain the differences.

  • Astro.com (from Astrodienst). A popular professional-grade chart-calculation website. Generates chart wheels and text reports. There is no AI option. No subscription is required for chart calculation. But I don't recommend taking screenshots of the chart wheels to upload to AI.
  • Astro-Seek. An ad-supported astrological calculator with a sprawl of free tools (transits, synastry, returns, and many others). Print-friendly text views designed for human reading. No AI integration but some charts have a helpful link to make it easy to "copy for AI."
  • Astro-engine.com. A newer consumer-oriented website. After you sign up, there's both a chart calculator and an "AI Cosmic Advisor" powered by Claude AI. Freemium with paid tiers ($9 Pro, $29 Premium).
  • AstroPrompt. Free web workbench and no account is required. Calculates the chart, then prepares the data and a suitable prompt. There's an AI chat window for the LLM of your choice (ChatGPT, Claude, Gemini, or others).

Calculation engine

All four use the Swiss Ephemeris. The math is equally good across them:

  • Astro.com. Swiss Ephemeris, based on NASA's JPL DE431 dataset. Better than 1/1000 of an arcsecond.
  • Astro-Seek. Swiss Ephemeris. Same accuracy class as Astro.com.
  • Astro-engine.com. Swiss Ephemeris. Claims 0.001 degrees of arc, covers 5401 BC to 5399 AD, with 66+ calculation modules including traditional and Hamburg School techniques at the Premium tier.
  • AstroPrompt. Based on Astrolog, which uses the Swiss Ephemeris under the hood. Same accuracy as the other three.

All four are calculation-accurate. The Swiss Ephemeris is the common denominator. Calculation is not the differentiator between these four.

AI interpretation

This is where the four diverge sharply:

  • Astro.com. No AI. You read the static reports yourself, or copy chart data into ChatGPT or another LLM.
  • Astro-Seek. No AI. Same as Astro.com. Just use it to copy and paste chart data.
  • Astro-engine.com. It has Anthropic's Claude wired into its "AI Cosmic Advisor." Allows two free questions a day on the free tier; more behind paid tiers. Claude AI is the only choice and you can't play with the prompts.
  • AstroPrompt. Offers you the choice of ChatGPT, Claude, Gemini, or any of eight LLMs. There's an AI chat for each. You can ask questions, follow-up questions, and even experiment with setting different prompts in a free Pro edition.

Cost and limits

  • Astro.com. Free for chart calculation. Expert reports sold separately.
  • Astro-Seek. Free for chart calculation. Ad-supported.
  • Astro-engine.com. Account required. The free tier has natal charts, five saved charts, horoscopes, and two Claude AI questions a day. A Pro tier at $9 a month offers synastry, predictive tools, API access. The Premium tier at $29 a month offers advanced techniques, including the Hamburg School.
  • AstroPrompt. No account required. No limit on free calculations. Nearly unlimited free use of AI chat for the lowest-cost LLMs (GPT-5 Mini, Gemini 3 Flash Preview, Grok 4.1 Fast, DeepSeek V3.2, subject to rate limits). Generous use of the expensive LLMS (OpenAI GPT 5.5, Anthropic Claude Opus, Gemini 3.1 Pro Preview), up to 30 questions total. If you never want to pay for premium AI, you can copy the data into any chat.

Audience

  • Astro.com. For professional and experienced astrologers who want reliable chart calculations displayed as chart wheels. Copy-and-paste to get AI chat.
  • Astro-Seek. For experienced astrologers who want every free tool in one place. Copy-and-paste to get AI chat.
  • Astro-engine.com. A polished user interface and an easy-to-use AI option. A wide range of astrology tools. Integrated AI chat and consumer-friendly.
  • AstroPrompt. An easy workflow from calculation to AI chat. Not as polished as astro-engine.com but more open for experimentation and customization. Good for professionals and students and users who want to tinker.

Data and privacy

  • Astro.com. Privacy-conscious by reputation. Birth data stored with an optional account. No AI.
  • Astro-Seek. No account required unless you want to store your data across sessions. Browser tracking for ad services. No AI.
  • Astro-engine.com. Not as much privacy. Requires an account (email, display name, password). Stores birth data, usage statistics, and AI Advisor conversation history. The privacy policy states AI Advisor questions and response previews are retained for 90 days for quality improvement and abuse prevention. Stripe for payments. Anonymous website analytics.
  • AstroPrompt. No account needed for free use. Birth data only stored on your own computer. The software developer gets anonymous usage tracking without any private info. For AI chat, the chart data and conversation goes to the AI provider you choose (OpenAI, Anthropic, etc,) governed by their privacy policies.

Quick comparison

  • Astro.com. The best free chart calculation website for chart wheels. No AI.
  • Astro-Seek. The most tools for free. No AI.
  • Astro-engine.com. A closed-platform consumer astrology app with optional Claude AI chats.
  • AstroPrompt. A workbench that's a bit clunky but combines calculations with AI chat for free.

How to use them

  • Astro.com. Excellent calculation. You handle the LLM yourself. The copy-paste step is cumbersome because the website is old. I don't recommend taking screenshots of chart wheels because ChatGPT and other LLMs often miss details.
  • Astro-Seek. Excellent calculation. You handle the LLM yourself. No built-in AI but an easy copy-paste workflow with your own AI platform.
  • Astro-engine.com. Excellent calculation. The AI step is integrated, but locked to Claude with a quota, and the prompts can't be seen.
  • AstroPrompt. Excellent calculation. Lots of control over calculation, prompts, and choice of LLMs.

AstroPrompt versus Astro-engine.com

Astro-engine.com is the most direct functional competitor to AstroPrompt. Both solve the same calculation-plus-AI problem with the same Swiss-Ephemeris math. Here are the differences, as I see them:

  • AI flexibility. Astro-engine.com locks you to Claude. AstroPrompt lets you pick any LLM from eight choices.
  • Prompt transparency. Astro-engine.com's prompts are hidden to users. AstroPrompt Pro exposes the prompts and documents them all at /prompts/.
  • Quota. Astro-engine.com caps free use at two AI questions per day. With AstroPrompt there's unlimited use if you copy and paste to your own LLM, nearly unlimited use of budget LLMs (subject to rate limiting), and free trial use of premium LLMs up to 30 questions total.
  • Account requirement. Astro-engine.com requires sign-up and stores conversation history server-side for 90 days. AstroPrompt requires no account and stores nothing about you on its own servers.
  • Pricing model. Astro-engine.com is freemium with $9 and $29 tiers. AstroPrompt is free for calculations, free for budget LLMs (subject to rate limits), free for premium LLMs for the first 30 questions, and totally free if you copy and paste to your own AI platform.

How to choose

Pick by the question you are answering:

  • For a chart wheel to read yourself, use Astro.com.
  • For the broadest set of free calculators in one place, use Astro-Seek.
  • For an all-in-one AI astrology product, with a friendly consumer interface, use Astro-engine.com.
  • For a workbench experience, with editable prompts and no account, use AstroPrompt.

The four are not all-or-nothing. Many practitioners use Astro.com for the trusted chart wheel and AstroPrompt for the AI workflow on the same chart. The important thing is they all do accurate astrological calculations.

What's next

Pick the tool and the workflow you like. The calculation-first approach that I advocate works with any of the four. If you know a calculation tool worth adding to this comparison, or spot a detail worth correcting, email me at hello@timecasters.com.