Biorhythm API: What It Is, How It Works, and How to Use It
A biorhythm API calculates physical, emotional, and intellectual cycles from a birth date. Learn how it works and how to integrate it.
TL;DR
- Biorhythm is a belief-based model for entertainment and reflection, not a validated basis for medical, financial, safety, or emergency decisions.
- A biorhythm API calculates the sinusoidal cycles (physical, emotional, intellectual) that begin at birth and repeat with fixed periods
- Unlike simple calculators, a biorhythm API provides interpretation, phase detection, forecasting, compatibility scoring, and multi-language support
- RoxyAPI covers 10 cycle types (3 primary, 4 secondary, 3 composite), readings, forecasts, critical days, compatibility, and every language the API ships in a single subscription
- Build a biorhythm integration into your wellness app in under 30 minutes with a single POST request
What is biorhythm theory
Biorhythm theory proposes that human performance follows predictable sinusoidal cycles starting from the moment of birth. The theory labels three primary cycles: the physical cycle repeats every 23 days, the emotional cycle repeats every 28 days, and the intellectual cycle repeats every 33 days. Each cycle oscillates between a peak (+100%) and a trough (-100%), crossing zero twice per period at what practitioners call critical days.
The mathematical foundation is straightforward. For any given day, you calculate the number of days since birth and apply a sine function: sin(2 * PI * daysSinceBirth / cyclePeriod). The result tells you where in the wave you are. When a cycle is above zero, the model calls it a positive phase. Below zero, it calls it a negative phase. Neither label measures actual performance or recovery. Zero crossings are transitions in the mathematical model. They do not establish increased error or accident risk.
What a biorhythm API does vs a simple calculator
A biorhythm calculator takes a birth date, runs the sine formula, and returns a number. That is roughly five lines of code. A biorhythm API does significantly more, which is why developers choose managed infrastructure over implementing the formula from scratch.
A production-grade biorhythm API provides phase detection (not just the raw value, but whether you are peaking, rising, at a critical crossing, or in recovery), trend analysis (is the value going up or down compared to yesterday), interpretation text (editorial prose explaining what the reading means for that day), and energy ratings (a composite score derived from all three primary cycles).
Beyond single-date readings, a full biorhythm API offers forecasting (multi-day projections with phase transitions highlighted), critical day detection (upcoming zero crossings across all cycles), compatibility scoring (overlay two birth charts and measure alignment), and multi-language support for global applications.
Ready to build this? RoxyAPI Biorhythm API gives you 10 cycle types, readings, forecasts, critical days, compatibility, and every language the API ships in one subscription. See pricing.
Why developers use a biorhythm API instead of building one
The sine formula is trivial. The infrastructure around it is not. Here is what you would need to build and maintain yourself if you chose to implement biorhythm calculation from scratch:
Interpretation layer. A display can pair each model value with a phase label and interpretive text. Frame the wording as entertainment or reflection, not evidence of real-world capacity.
Internationalization. If your app serves a global audience, you need translations for phase labels, interpretations, and advice text. The RoxyAPI Biorhythm API supports English, German, Spanish, French, Hindi, Portuguese, Russian, and Turkish out of the box.
Multiple endpoints for different use cases. A reading endpoint covers one day. But dating apps need compatibility scoring. Productivity apps need multi-day forecasts. Reflection apps can display model zero-crossing dates. Building each of these as a separate, well-documented endpoint with proper input validation takes weeks.
Maintained infrastructure. API versioning, rate limiting, caching, documentation, uptime monitoring, and error handling. These are not biorhythm problems, but they consume more engineering time than the core calculation ever will. You also need ongoing maintenance as your user base grows: scaling concerns, cache invalidation strategies, and keeping documentation in sync with actual behavior.
Structured data for AI agents. If your app integrates with LLMs, AI agents, or chatbots, you need well-typed JSON responses with consistent field names and rich descriptions. A biorhythm API designed for AI consumption includes MCP tool definitions, OpenAPI specs, and response schemas optimized for agent reasoning.
10 cycle types in the API
Most biorhythm calculators stop at the 3 primary cycles. The RoxyAPI Biorhythm API calculates 10 distinct cycle types organized into three tiers:
Primary cycles (classical biorhythm):
- Physical (23-day period): theory label for the physical curve
- Emotional (28-day period): theory label for the emotional curve
- Intellectual (33-day period): theory label for the intellectual curve
Secondary cycles (extended biorhythm):
- Intuitive (38-day period): gut feelings, subconscious perception
- Aesthetic (43-day period): creative expression, appreciation of beauty
- Awareness (48-day period): self-reflection, mindfulness, perception clarity
- Spiritual (53-day period): inner peace, sense of purpose, connection
Composite cycles (derived from primary pairs):
- Passion (physical + emotional average): romantic energy, drive
- Mastery (physical + intellectual average): skill execution, athletic strategy
- Wisdom (emotional + intellectual average): empathetic reasoning, judgment
Each cycle includes a value from -100 to 100, raw sine value, 8-state phase detection, trend direction, day position within the cycle, days until the next peak, trough, and critical crossing, plus a full interpretation paragraph.
An endpoint for every biorhythm use case
The Biorhythm API reference documents every endpoint, each designed for a specific integration pattern:
| Endpoint | Method | Use Case |
|---|---|---|
/reading | POST | Complete analysis for a single date |
/forecast | POST | Multi-day projection (up to 90 days) |
/critical-days | POST | Upcoming zero crossings (up to 180 days) |
/compatibility | POST | Alignment score between two people |
/phases | POST | Lightweight cycle status for all 10 cycles |
/daily | POST | Seeded daily snapshot for check-in features |
The /reading endpoint is the most comprehensive. Here is a request you can run:
curl -X POST https://roxyapi.com/api/v2/biorhythm/reading \
-H "Content-Type: application/json" \
-H "X-API-Key: YOUR_API_KEY" \
-d '{"birthDate":"1990-07-15","targetDate":"2026-04-11"}'Read the response fields against the current Biorhythm API reference. The cycle objects contain the calculated value, phase, trend, and interpretation for the requested date.
This response gives you everything needed to render a biorhythm dashboard, power an AI chatbot response, or drive notification logic in a wellness app.
How biorhythm calculation works under the hood
The core formula for any biorhythm cycle is:
value = sin(2 * PI * daysSinceBirth / cyclePeriod) * 100Where daysSinceBirth is the integer count of days from the birth date to the target date, and cyclePeriod is the fixed length of that cycle (23, 28, 33, 38, 43, 48, or 53 days depending on the cycle type).
Composite cycles average the raw sine values of their two parent cycles before converting to a percentage. For example, the Passion cycle is:
passion = ((sin(2*PI*days/23) + sin(2*PI*days/28)) / 2) * 100Mastery averages the physical and intellectual curves; wisdom averages emotional and intellectual. Average the raw sine values before rounding the displayed percentage. A composite is a sum of two waves, not a new single-period sine wave. Its complete pattern repeats over the least common multiple of its parent periods. These mathematical labels do not measure skill, judgment, or relationship quality.
For a reflection dashboard, use /phases for a compact single-date display and /forecast for a calendar of model values. Let users choose which curves appear first. A neutral notification can identify a model phase or zero crossing; it should not assign tasks, predict accidents, or recommend changes to treatment, exercise, travel, or financial decisions.
Phase detection classifies the rounded model value into eight display states:
| Phase | Rounded value | Meaning in the model |
|---|---|---|
| Peak | 90 to 100 | Highest band |
| High | 50 to 89 | High positive band |
| Rising | 10 to 49 | Positive band |
| Critical ascending | -9 to 9, value not below the previous day | Near-zero band |
| Critical descending | -9 to 9, value below the previous day | Near-zero band |
| Falling | -49 to -10 | Negative band |
| Low | -89 to -50 | Low negative band |
| Trough | -100 to -90 | Lowest band |
The phase names rising and falling describe value bands; the separate trend field describes direction. A positive value can be moving downward. Keep the band and direction separate in a dashboard, and label both as model output rather than measured capacity.
The energy rating condenses the three primary cycle values into a single 1-10 integer score, making it easy for apps to display a quick daily snapshot without overwhelming users with raw data.
Frequently Asked Questions
Q: What is a biorhythm API? A: A biorhythm API is a web service that calculates biorhythm cycle positions from a birth date and target date. It returns structured data including cycle values, phase classifications, trend directions, interpretive text, and energy ratings. Developers integrate biorhythm APIs into wellness apps, dating platforms, productivity tools, and AI agents.
Q: How accurate is biorhythm calculation? A: The mathematical calculation is deterministic and precise. Given a birth date and target date, the sine function produces an exact value. The RoxyAPI Biorhythm API includes a gold standard test suite verifying calculation accuracy. Calculation tests verify the formula, not real-world predictions. Use the output for entertainment or reflection, never to make medical, financial, safety, or emergency decisions.
Q: Is there a free biorhythm API? A: RoxyAPI offers a Starter plan that includes access to all biorhythm endpoints along with every other domain in the platform. Each plan includes 50,000 to 3,000,000 requests per month depending on the tier. Check the pricing page for current rates.
Q: Can I use a biorhythm API in a dating app?
A: Yes. The /compatibility endpoint accepts two birth dates and returns per-cycle alignment scores, an overall compatibility percentage, relationship rating, strengths, challenges, and practical advice. This is specifically designed for dating platforms, couples coaching apps, and relationship wellness tools.
Q: What languages does the biorhythm API support?
A: Responses are localized into every language the API ships, including English, German, Spanish, French, Hindi, Portuguese, Russian, and Turkish. Pass the lang query parameter (e.g., ?lang=es) to receive interpretations, phase labels, and advice text in the specified language.
Build with biorhythm data today
A biorhythm API transforms a simple mathematical formula into structured model output for entertainment and reflection. With 10 cycle types, 8 phases per cycle, 6 specialized endpoints, and localization in every language the API ships, the RoxyAPI Biorhythm API covers every biorhythm integration scenario developers encounter. Whether you are building a wellness dashboard, powering a reflective journaling assistant, or adding a compatibility feature to a dating app, structured biorhythm data is one POST request away.
The biorhythm calculation API is part of a single subscription that includes every domain RoxyAPI offers. One API key, one rate limit pool, one set of documentation. Explore the full API reference or check pricing to get started.