Short answer Numbers like “one Navkarsi reduces 100 years of hell-life” are not found in the Agamas or Tattvartha Sutra. Jain scriptures describe that tapas weakens karmas, but they do not give fixed numeric conversions of “years of Narak reduced” for specific practices. So there is no authentic, universally accepted figure for Chauvihar Upvas or Tivihar Upvas either.

What the traditions do say (simple, reliable points)

• Intensity (from lighter to stricter): Navkarsi (first meal after sunrise) < Tivihar Upvas < Chauvihar Upvas.
• Therefore, the spiritual fruit (punya/paap‑kshaya) of Chauvihar Upvas is greater than Tivihar Upvas, and both are greater than Navkarsi—but scripture does not quantify it in “years.”
• Shvetambar and Digambar both uphold the principle; small procedural differences exist (e.g., about taking boiled water in daylight). None give fixed “year” numbers.

Clear definitions (for context)

• Navkarsi: Taking the first meal only after about 48 minutes after sunrise, with right restraint and mindfulness.
• Tivihar Upvas: Fast without food; boiled/filtered water allowed only in daylight (stricter variants differ by tradition).
• Chauvihar Upvas: Fast without food and without water after sunset; in its strict form, no water at all for the fast period. This is stricter than Tivihar.

Essence to remember

• In Jain Dharma, bhav (inner intention), careful observance, and non‑violence are primary. Exact “years reduced” claims come from later popular sayings or local pravachans and vary; they are not a standard scriptural measure.

For simple explanations of these fasts, you can read:

• Chauvihar vs. Tivihar basic differences
• What is Choviar (Chauvihar)
• Overview of fasting methods