Calculation and interpretation
How a birthday becomes a card, and how the card becomes a reading.
By Cassidy Rice · Updated August 17, 2026 · Editorial policy
Quick answer
The birthday gives the card. The suit gives the life domain. The rank gives the movement. The ruling card, timing card, and relationship context show how the pattern expresses in a real person. Same birthday always produces the same birth card.
Core structure
52 cards
The deck is treated as a calendar-like structure with one card for each week of the year.
4 suits
Hearts, Diamonds, Clubs, and Spades describe domains of life: feeling, value, mind, and work.
13 ranks
Aces through Kings describe movement inside a suit, from initiation through mastery.
Fixed birthday map
A birth card is calculated from the birthday. It is not chosen by a quiz or random draw.
Worked example
Take a public calendar date: January 15. In this system the date resolves to the Queen of Diamonds as birth card — the same result every time the math is run. The year is not required for the birth card itself; year feeds timing layers when you ask about a specific chapter.
- Input. Month and day only for the birth card; optional year for ruling-card context and periods.
- Map. The date lands on one of 52 fixed deck positions. December 31 is the Joker boundary; February 29 maps normally to the 9 of Clubs.
- Read structure. Suit = diamonds (values & resources). Rank = Queen (stewardship, refinement, influence inside that suit).
- Add ruling card. Zodiac-linked planetary rulership colors how the Queen of Diamonds tends to express for that birth chart layer.
- Test in life. Compare the language to real behavior. Keep what matches; drop what does not. The card is a hypothesis generator, not a verdict.
You can open the live page for that date at /born-on/january-15 or re-run any birthday in the birth card calculator. If two tools disagree on the same system rules, trust the one you can audit — and tell us on the contact page.
Birth-card formula
The live calculator uses this mapping. You can check the math by hand, then confirm the card in the 366-row CSV. Year is not used for the birth card. Paid books teach permutation history, yearly spreads, and interpretation. They do not change this public formula.
- Solar value.
sv = 55 − (2 × month + day) - Wrap. If
svis 0 or less, add 52. - Lookup. Map
svthrough the fixed 52-card solar table. The CSV is the complete table. - Public exception. December 31 is the Joker (solar value 0). The wrap would otherwise collide with January 1 (King of Spades). We do not force December 31 into a standard 52-card result.
Exception rules
- February 29 maps normally to the 9 of Clubs. Leap day is in the table, not skipped.
- December 31 is the Joker boundary, not King of Spades.
- Invalid calendar dates are rejected. They are not remapped.
Version history
- 2026-08-15 — Dataset version 2026-08-15. Full 366-row CSV published.
- 2026-08-17 — Formula, exception rules, and test vectors published on this page. Birth-card results unchanged.
Open data
Download the 366-date Cardology map
The CSV contains 366 rows, one for every month-and-day combination. Each row includes the card code, rank, suit, solar value, canonical card URL, birthday URL, exception rule, claim classification, and dataset version. February 29 maps to the 9 of Clubs. December 31 is preserved as the Joker boundary rather than being forced into a standard 52-card result.
Download CSV (366 rows)How to cite this dataset
Card Blueprints. Cardology Birthday Map: 366 Date-to-Card Mappings. Version 2026-08-15. https://cardblueprints.com/data/cardology-birthday-map.csv
The table publishes deterministic date-to-card mappings used by the live calculator. Personality, relationship, and life-pattern interpretations are separate: interpretive meanings are Cardology pattern language, not experimentally established facts.
For the public release notes, exceptional-date checks, and explanation of why the table is auditable, read Read the 366-date publication note.
Interpretation order
Start with what is fixed: the birthday, the card, the suit, and the rank. Then read the range: balanced expression, under-expression, over-expression, gift, shadow, timing, and the person or relationship involved.
The ruling card colors how the birth card comes through. A period card names the chapter. Compatibility adds another person’s pattern, which is where attraction, friction, support, and repetition become easier to see.
A strong reading moves in that order: calculate the card, read the structure, compare it with the person, then test whether it explains the behavior or dynamic in front of you.
What we do not claim
Cardology on Card Blueprints is a pattern-recognition system for self-awareness and entertainment. It describes tendencies, not fate. It is not medical, psychological diagnosis, legal, or financial advice. Paid reports use the same deterministic engine as the free tools; interpretation prose is labeled as interpretation.
Test vectors and corrections
The public birthday map is the formula. Same month and day always return the same birth card. Check these known rows against the calculator:
- January 1 → King of Spades (solar 52)
- January 15 → Queen of Diamonds (solar 38)
- February 29 → 9 of Clubs (leap-day row, solar 22)
- March 21 → 2 of Diamonds (solar 28)
- July 4 → Jack of Diamonds (solar 37)
- October 31 → 4 of Hearts (solar 4)
- December 25 → 6 of Hearts (solar 6)
- December 30 → Ace of Hearts (solar 1)
- December 31 → Joker (year-end boundary; public override)
Dataset version is dated on this page. If a mapping is wrong, email contact with the date and expected card. We correct the CSV and this page rather than silently changing live reports.