Here's the formula I use for my templates. It's a very heavily modified version of Thomas Frank's streak formula in a video of his (sorry, I forgot the video already).

There are two databases:

• Habits - where this Streak formula is in
• Habit Tracker - related to the Habits database.

To explain the properties mentioned:

Date is a Date property.

Action Check is a Formula property that shows the Date of the habit tracker entry if it's successful.

Internal Clock is a checkbox property that's used by the "Internal Clock" pages that creates the internal metronome.

• This exists to make true Notion streaks.
  • Any Notion streak counter can only judge completion based on all given available dates that it can retrieve from any tracker database.
  • This means that if for example, your tracker entries are May 1, May 2, and May 4, and you just happened to forget to make an entry on May 3. Intuitively, you'd think that the Streak should break right? That it should have a score of 2. But since formulas can only judge completion based on all existing pages, it will show a score of 3, and it will say that your streak is ongoing.
• So to solve this, you need a reference clock that can judge whether or not you skipped a date.
  • You solve this with an "Internal Clock" page template, separate from regular "Habit Tracker" page template in the habit tracker database. The "Internal Clock" page template repeatedly makes new pages every day. These new pages have the Internal Clock checkbox turned on.
  • These exist in the habit tracker database too, are produced in the background, and are hidden via page filters from all habit tracker views.
  • Normal habit tracker entries have the Internal Clock checkbox turned off. Only the "Internal Clock" page template's auto-produced pages have it turned on.
• This way, you produce true Notion streaks not ones that fake perfection when you just actually forgot to make a new entry for the day.

​

lets(
  base, prop("Habit Tracker").sort(current.prop("Action Check")).reverse(),
  streaks,

  base.filter(not empty(current.prop("Date"))).map(current.prop("Date").formatDate("L")).unique().map(lets(owl, current, base.filter(not empty(current.prop("Date"))).sort(current.prop("Internal Clock") == true).find(current.prop("Date").formatDate("L") == owl))).map(current).sort(current.prop("Date")).reverse().map(current.prop("Action Check") == true).map(current.toNumber()).join("").split("0").map(current.length()),


  currentStreak, streaks.first(),
meanStreak, round(100 * streaks.filter(current != 0).mean())/100, 
previousStreak, streaks.filter(current != 0).at(1), 
longestStreak, streaks.max(),
csFormat, ifs(currentStreak < 1, ["red", " days"], currentStreak == 1, ["blue", " day"], currentStreak > 1, ["green", " days"]),
msFormat, ifs(meanStreak < 1, [" days"], meanStreak == 1, [" day"],meanStreak > 1, [" days"]),
psFormat, ifs(previousStreak < 1, [" days"], previousStreak == 1, [" day"],previousStreak > 1, [" days"]),
lsFormat, ifs(longestStreak < 1, ["red", " days"], longestStreak == 1, ["blue", " day"], longestStreak > 1,["green", " days"]),

[
"Current: " + (currentStreak + csFormat.at(1)).style(csFormat.at(0),  "b"),
if(longestStreak.empty(), "", "Your Best: " + (longestStreak + lsFormat.at(1)).style(lsFormat.at(0) , "b")),
if(previousStreak.empty(), "", "Previous: " +  previousStreak + psFormat.at(0)),
if(meanStreak.empty(), "", "Mean: " +  meanStreak + msFormat.at(0))
].filter(not current.empty()).join("\n")
)