In the Bible, Daniel is described as fasting for three weeks (21 days) during one recorded period and for 10 days during another.

Main fasting periods

  • In Daniel 10:2–3, he says he mourned and abstained from rich food, meat, wine, and lotions for “three full weeks,” which is 21 days.
  • In Daniel 1:12–15, Daniel asks to be tested for 10 days on vegetables and water instead of the royal food and wine.

Why people say “21-day Daniel Fast”

  • Many modern Christian practices of the “Daniel Fast” are modeled on the three-week period in Daniel 10, so churches and individuals commonly observe a 21‑day Daniel Fast today.
  • Some also note the 10-day test in Daniel 1 as another biblical pattern for a shorter Daniel-style fast.

Quick Scoop (SEO-style notes)

  • Focus phrase “how long did Daniel fast in the Bible” usually points to the 21 days in Daniel 10:2–3.
  • For Bible study or forum discussions, it is accurate to say: Daniel fasted 10 days in Daniel 1, and 21 days in Daniel 10, with another unspecified fast in Daniel 9.

TL;DR: Daniel fasted 10 days in Daniel 1 and 21 days in Daniel 10; the popular “Daniel Fast” today is typically a 21‑day fast patterned on the three‑week mourning in Daniel 10.

Information gathered from public forums or data available on the internet and portrayed here.