How Nava Calculates

Two independent engines, the classical conventions we follow on purpose, and the printed almanacs we check ourselves against.

நவ எவ்வாறு கணிக்கிறது — இரண்டு தனித்தனி கணிப்பு முறைகள், நாங்கள் வேண்டுமென்றே பின்பற்றும் மரபு மரியாதைகள், எங்களையே சரிபார்த்துக்கொள்ளும் அச்சுப் பஞ்சாங்கங்கள்.

Two calculation systems

Nava offers two independent engines and always shows which one is active. The two traditions genuinely disagree on some days — that is the point of offering both, not a defect in either. Neither is the “correct” one: the one that is right for you is the one the almanac your family already follows is computed from. You can switch between them in your profile at any time.

What each engine was checked against

Vākya is verified against printed almanac data from two publishers — sources that print ghati–vighati only — and it reproduces those printed values. Measured against wall calendars that print actual clock times (Chennai 395 days, Coimbatore 377 and Delhi 363 — three complete years — plus Mumbai and 158 days of a US edition for New Jersey), the tithi or nakshatra named for the day matched the printed page on 2,664 of 2,666 comparisons. The two that differ are days where a limb ends within a minute of sunrise, so the page and the calculation name the limb on either side of the same boundary.

The Tamil calendar date matched on every one of the 1,344 printed days of the 2026-27 editions we have been able to check.

Thirukanitha is checked against published drik panchangam data for Chennai (2026) and Lucknow (2025) — 725 days, with every tithi, nakshatra, moon-rasi and paksha matching, and sunrise matching within seconds.

Two calendars, side by side

A Hindu date has two different months, and Nava computes both. The one it leads with is the Souramana (solar) Tamil month — Chithirai, Vaikasi, Aadi and so on — which changes when Surya enters a new zodiac sign. Nava applies the Tamil Nadu convention specifically: the month begins on the day of the sankranti if that moment falls before sunset, and otherwise the next day. Kerala and coastal Karnataka are also solar but resolve that boundary differently (Kerala uses an aparahna rule), so a small number of days each year will not match an almanac printed for those regions.

Nava also computes the Chandramana (lunar) month — Chaitra, Vaisakha, Ashadha — which runs from one new moon to the next (amanta reckoning, as followed across South and Western India), from the same engine you have selected. It is deliberately not displayed next to the Tamil month. A Tamil almanac does not print one: its columns are the solar month and day, the tithi and the nakshatra, and the lunar cycle is carried by the tithi and paksha you already see. Showing two month names side by side would leave you with no way to tell which one is yours.

One lunar fact the solar month cannot express does get shown. Roughly every 32½ months a lunar month contains no solar sankranti at all; that month is an Adhika (intercalary) month, and it is why some festivals fall a month later in those years. On those days — and only those — Nava shows a small Adhika Masa label with the lunar month it applies to. The most recent began on 17 May 2026 (Adhika Jyeshtha). The same label appears for the far rarer Kshaya month, where one lunar month absorbs the next one’s name (in the years Nava covers, 1900 to 2100, that happens only twice: late 1963 and January 1983).

How a festival gets its date

The lunar festivals are detected from the lunar month, not from the solar month as an approximation of it. Ugadi, Sri Rama Navami, Ratha Saptami, the Navaratri days, Deepavali and Naraka Chaturdashi, Gayatri Japam and Sama Veda Upakarma each name the lunar month they actually belong to, and an Adhika month is excluded — the correction that stops a festival landing a whole month early in the years where the lunar month it belongs to is doubled. Every one of those months was read off the printed almanacs rather than assumed, and each is checked against 952 transcribed almanac days on every change. That check covers the festivals a transcription actually names — about twenty of them — not every entry in the catalogue; the rest rest on the rule as stated rather than on a printed date we can point to.

A festival is also placed on the day the tithi prevails, not merely the day it happens to touch sunrise. Amavasya observances and their family are judged at aparahna (about 70% of the way through daylight); Pradosham is judged across the 90-minute pradosha kala that begins at sunset, because Trayodashi can begin after one sunset and end before the next and so prevail at neither. Where a tithi covers two such windows on consecutive days, the later day is taken. These are the almanac’s own conventions.

Traditional conventions we deliberately follow

• Vākya nazhigai origin. Ghati–vighati end times in the Vākya system are counted from sunrise as the printed Tamil almanac defines it — Surya’s geometric centre on the true horizon, not the refraction-corrected civil sunrise a weather app shows — so the ghati values you see match the book. Thirukanitha keeps the civil convention, which is the one its own published sources use, so the two systems print sunrise a few minutes apart on purpose.
• One instant, expressed locally. A tithi or nakshatra ends at a single moment everywhere on Earth. The printed almanac solves that moment once, for its own base town in Tamil Nadu, and each city edition prints it in local time and local ghati — which is why its Chennai, Mumbai and New Jersey pages carry the same end times once converted to a common clock. We do the same: the end times you see are the same instant a reader of the printed book sees, converted to your clock, while sunrise, sunset, horai, the kalams and the day strips remain your own city’s.
• The Tamil month begins by your own sunset. A solar month starts on the day Surya enters the new sign if that happens before sunset, and on the next day if it happens after. Sunset is local, so two cities can start the month a day apart — and the printed editions do exactly that: for August 2026 the Chennai page runs Adi to a 32nd day while the Coimbatore page has already begun Avani, because Surya entered Simha at 18:31, between Chennai’s sunset (18:26) and Coimbatore’s (18:37). We follow your city, as the book does.
• The kalams divide your actual daytime. Rahu kalam, Yamagandam and Gulikai are the classical eight equal parts of sunrise-to-sunset, one assigned to each by weekday. That is why a block runs about 92 minutes at Chennai in August rather than a tidy 90 — the day is 12 hours 20 minutes. The familiar “Monday 7:30–9:00” table is the same rule flattened onto a nominal 6am–6pm day.
• Vara turnover at sunrise. The weekday for scoring changes at sunrise, not midnight, exactly as in tradition.
• Rahu as the mean node. Rahu and Ketu positions use the mean lunar node, the convention of classical Vimshottari dasha software; Ketu is opposite Rahu.
• Houses: by sign in the chart, by bhava in the reading. The rasi chart draws each house as one whole sign, counted from the Lagna’s sign, and the reading’s aspects and the kendradi part of shadbala (inside Position) count by sign too. Your reading, the yogas in your chart, the Planetary Positions table and Your Period count a house from the Lagna by the Sripati bhava, measured from the Lagna’s degree. A planet can then sit one house (at high latitudes, two) away from where the chart draws it; the table shows its count by sign as well.
• Place data from GeoNames. The cities you can pick, their coordinates and time zones come from GeoNames, used under the Creative Commons Attribution 4.0 licence. A neighbourhood whose sunrise is within half a minute of its town’s shares the town’s point.

Outside India, and how far from the equator

• Times are the city’s clock. Every time on a day’s page is in the time zone of the city you picked. When your device is set to a different zone, the page says which clock it is showing.
• Vākya end times are one instant everywhere. The Vākyakaraṇa tables give each tithi and nakshatra end as a single moment for the whole almanac, not one per city, so it ends at the same moment for every city, and Nava shows that moment on your city’s clock. Sunrise, and so the tithi at sunrise, is your own city’s. The Thirukanitha engine computes each end time from true positions instead.
• The Tamil date can differ between the engines. Each engine places Surya’s entry into a sign at its own moment, so their Tamil dates can differ by a day, and far from India by up to two. On 23 September 2026 Chennai reads Purattasi 6 by Vākya and Purattasi 7 by Thirukanitha; Honolulu reads Purattasi 6 and Purattasi 8.
• Places within 60° of the equator. Nava calculates for places from 60° north to 60° south. Further toward the poles Surya skims the horizon, sunrise and sunset can fall on either side of midnight, and nearer the poles Surya stays up, or down, for whole days, so the day the panchangam is built on no longer holds. Those places are not offered in the city list, and Nava does not calculate for them. Oslo, Stockholm and Saint Petersburg are inside the range; Helsinki, Anchorage and Reykjavik are outside it.

Gowri Panchangam, Abhijit, Durmuhurtham, Varjyam

The Gowri day and night sequences are the fixed weekday tables of the Tamil tradition, including the Saturday-night table’s repetition of Soram. Abhijit muhurtham is the 8th of the fifteen day-muhurtas, omitted on Wednesdays per tradition. Durmuhurtham windows are the classical weekday muhurtas. Varjyam (nakshatra thyajyam) starts after the tabled ghatis of each nakshatra’s own span and lasts four ghatis of that span, timed by whichever engine is active so it always agrees with the nakshatra end times shown.

The auspiciousness score

Classical jyotisha has no 0–100 number. Nava’s score is a documented, normalised mapping of how a muhurta is traditionally judged: the Amritadi yoga (weekday and star: Amrutha, Siddha, Marana) and the nakshatra and tithi classes dominate; nithya-yoga and karana refine; Rahu kalam, Yamagandam and Gulika kalam are strong time penalties. A severe dosha — a Marana yoga, an active kalam — hard-caps the score, so good factors are never allowed to dilute it away.

The personal score adds Tarabalam, Chandrabalam, Chandrashtama, Sade Sati and your running Vimshottari dasha–bhukti, judged from your own Lagna where your birth details allow a full chart.

Nava is a religious and cultural reference.