Most ancient civilisations had to choose between a strict lunar calendar (months track the Moon, but the year drifts through seasons) and a strict solar calendar (year fixed to seasons, but lunar phases drift across days). The Hindu tradition chose neither — it built a *lunisolar* system that anchors months to the Moon and the year to the Sun, with one elegant correction mechanism: *Adhik Maas*. Rarer still, in some years that correction is balanced by a *Kshaya Maas*. This article explains how the two interact.
✦ The Underlying Numbers
- ✦**Synodic month** (new moon to new moon) ≈ 29.531 solar days.
- ✦**Tropical year** (one full cycle of seasons) ≈ 365.242 solar days.
- ✦**12 synodic months** ≈ 354.367 days.
The lunar year is therefore about 10.875 days short of the solar year. Without correction, after just three years the lunar months would slide back by a month — Holi (a spring festival) would land in winter; Diwali (an autumn festival) would slip into late summer.
✦ The Solar Year — Saura Maasa
The solar (saura) calendar tracks the Sun's passage through the 12 sidereal rashis. Each transit (*sankranti*) marks the start of a saura maasa: - Sun enters Mesha (Aries) → Mesha sankranti, beginning of the solar year in many traditions. - Sun enters Karka (Cancer) → Karka sankranti / Dakshinayana (Sun moves south). - Sun enters Makara (Capricorn) → Makara sankranti / Uttarayana (Sun moves north).
Because Earth's orbit is elliptical, the Sun's apparent speed varies: a saura maasa is 29.45 days when the Sun is in Dhanu (December), up to 31.46 days in Mithuna (June). The 12 saura maasas total exactly one tropical-sidereal year (~365.25 days).
✦ The Lunar Year — Chandra Maasa
The lunar (chandra) calendar tracks the Moon's cycle of phases. Each chandra maasa runs: - *Amanta* convention (South India, Maharashtra, Gujarat): from one Amavasya to the next. - *Purnimanta* convention (North India, Nepal): from one Purnima to the next.
Both label tithis identically; only the month-name boundary differs. A lunar year of 12 chandra maasas runs ~354.36 days.
✦ The Adhik Maas Rule
The classical rule (from *Surya Siddhanta* and codified in *Dharmasindhu*): a chandra maasa is declared *Adhik* (extra) if it contains no *sankranti* — i.e., the Sun stays in the same sidereal sign for that whole lunar month.
This typically happens once every 32 to 33 lunar months, or roughly every 2.7 solar years. The Adhik Maas takes the name of the chandra maasa it duplicates: e.g., *Adhik Shravana* in 2023 paired with the regular Shravana that followed.
The doubled month is also called *Mala Maasa* ("dirty month") in some North Indian traditions because it contains no festivals (those follow the regular *Nija* maasa). It is also called *Purushottama Maasa*, considered sacred to Lord Vishnu — devotees treat it as an opportunity for additional vratas, donation and pilgrimage.
✦ The Rare Kshaya Maas
The opposite case can also happen: a single chandra maasa contains *two* sankrantis — meaning the Sun changes signs twice within one lunar month. The classical rule then declares that month a *Kshaya Maasa* (diminished month) — its name is dropped from the calendar.
Kshaya months are extremely rare — about once every 19 to 141 years, depending on counting convention. They occur because near aphelion (Earth farthest from Sun, around July) Earth moves slowly and saura maasas are long, while near perihelion (Earth closest, around January) Earth moves quickly and saura maasas are short. When a chandra maasa happens to fall entirely within a fast-Sun period, two sankrantis can occur within it.
When a Kshaya Maas happens, an Adhik Maas is also inserted in the same year (sometimes earlier, sometimes later in the year) to keep the long-term lunar-solar drift bounded. The combination is called *Adhik–Kshaya Yuga* and complicates festival timing for that year — most communities follow the principle that the lost month's festivals are observed in the preceding or following month, with regional variations.
✦ Why This Matters Today
Even with all these adjustments, the lunisolar calendar remains within a ~30-day band against the solar year. The price of this elegance is that: - A festival's exact English date varies year to year (often by ±10 days, occasionally by ±20). - In Adhik Maas years a "second Shravana" or "second Bhadrapada" can arrive — many people are confused about which one carries the year's principal festivals (the *Nija* maasa, not the Adhik). - Personal vrats begun in a Nija maasa are typically completed in the corresponding Nija — Adhik insertions don't break a multi-month vrata.
Understanding Adhik and Kshaya Maas turns the Hindu calendar from a "shifting" curiosity into what it actually is: one of the most carefully designed timekeeping systems in the world — built to honour the Moon's beauty without losing the Sun's discipline.