# How many days has it been? Counting from a date, and why the counter works

> Three months is 89 days once and 92 another time. The starting day usually does not count. And a counter can turn an intention into something you would rather not break - as long as it is not the only thing it shows.

"I have been on a diet since the first of September." A simple sentence with
three questions behind it: how many days is that, when does it end, and what
is the counter actually measuring.

## The starting day counts as zero

This is not only a calculator convention. Polish law counts the same way: for
a deadline set in days, the day on which the event happened is not counted
(art. 111 of the Civil Code). A contract signed on Monday with a seven day
deadline ends the following Monday, not on Sunday.

In practice: something that began yesterday has lasted one day. On the
starting day the counter shows zero, which is correct even though we would
say "day one" out loud.

## Three months is not one number

A calendar month runs from 28 to 31 days, so "three months" means different
things depending on when you start:

| start | end | days |
|---|---|---|
| 1 January | 1 April | 90 |
| 1 February | 1 May | 89 |
| 1 June | 1 September | 92 |
| 1 July | 1 October | 92 |

Three days of spread. That is why the counter takes a month as 30 days and
three months as 90: then "three months" and "90 days" mean the same thing and
there is no argument about whether the plan is done.

Official deadlines work the other way round: there the calendar decides, and a
deadline set in months ends on the day with the same number in the final
month.

## Why count at all

A counter changes what an intention is. Instead of "I want to lose weight"
there is a number that grows by itself and that you would rather not reset -
the same mechanism that keeps people from breaking a streak in a language app.

It is worth knowing the other side of it. In the 2010 study by Lally and
colleagues, missing a single day had **no material effect** on habit
formation; repetition over time was what mattered. A counter that shows only
an unbroken run therefore teaches something the data does not support: that
one slip sends you back to the beginning. Which is why resetting our counter
keeps the record, and why a plan shows a percentage rather than a bare number
of days.

More on how long habit formation actually takes - a median of 66 days, not 21
- is in a separate piece: [how long to form a
habit](/blog/how-long-to-form-a-habit).

## What is worth counting

- **Things already under way.** No need to wait for Monday: put in a date in
  the past and the counter starts with what you have already done.
- **Things with no end.** "Not smoking since" needs no plan to make sense.
- **Things with a deadline.** A 30 day challenge, three months without
  alcohol, a hundred days of study: there the percentage says more than the
  raw number.

What not to count: anything whose progress is measured in money or in
repetitions. Those are goals, not counters - a goal takes a value, a counter
takes only a date.

## Count your own days

The [day counter](/en/tools/days-since) works without an account: enter a
date, optionally a plan, and see the days behind you and the percentage of
the plan. If you are counting forward - to the holidays, to Christmas, to an
exam - that is what the [countdown](/en/tools/days-until) is for.

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Źródło: https://ordiarion.com/blog/counting-days-since-a-date