Guest-host qi overlay (客主加临, Ke-Zhu Jiaohui) is the classical method of superimposing the annually rotating guest qi (客气) onto the fixed seasonal host qi (主气) for each of the year's six 60-day steps. The result reveals which climatic energy actually dominates a given two-month window — not merely which season it is, but what atmospheric flavour the year has layered on top of that season.
Host qi as the fixed baseline
Host qi (主气) is the fixed baseline. Every year, the same six energies step through the calendar in the same order: Jueyin Wind-Wood opens spring, Shaoyin Sovereign Fire carries early summer, Shaoyang Ministerial Fire governs high summer, Taiyin Damp-Earth rules late summer, Yangming Dryness-Metal arrives with autumn, and Taiyang Cold-Water closes the year in winter. This sequence, laid out in 《素问·六微旨大论》, never changes — it is the earth's own seasonal heartbeat.
Guest qi as the annual rotation
Guest qi (客气), by contrast, rotates. Its position in each year's six-step sequence is determined by the year's Sitian (司天) qi, which itself derives from the earthly branch of the sexagenary cycle. Because guest qi shifts from year to year, its overlay onto the fixed host qi produces a different interaction every time. When guest and host share the same element the climate is amplified; when they clash, the period may carry conflicting tendencies — warmth arriving too early, or cold lingering past its season. 《素问·至真要大论》 discusses these interactions in detail, classifying them as harmonious, mutually generating, or mutually restricting.
How TianJi evaluates the overlay
TianJi computes the overlay for the exact date you enter. It first resolves the host qi for the current 60-day step from the calendar, then resolves the guest qi from the year's Sitian position, and finally evaluates the relationship between the two — whether they reinforce, moderate, or conflict with each other. This interaction is what gives each TianJi daily card its specific seasonal character, and every computed overlay is traceable to a Suwen passage.
Educational use only
The overlay is a wellness-education tool, not a diagnostic instrument. It tells you, for example, that a given period carries amplified dampness or unexpected dryness, so you can adjust diet, sleep, and activity accordingly. It does not predict illness, identify disease, or replace the judgement of a qualified practitioner.