# Days until the 1st

Counts the days from today, or any date you choose, to the next 1st of a month, with its date and the 1st after it.

- Page: https://www.acalculator.org/days/days-until-the-1st
- JSON spec: https://www.acalculator.org/days/days-until-the-1st.json
- Version: ad94caed6997

## Default answer

Example with the default inputs (Count from October 19, 2026) on the example date Monday, October 19, 2026: From October 19, 2026, there are 13 days until the 1st, Sunday, November 1, 2026.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| from | Count from | The date to count from. Today, unless you change it. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| days | Days until the 1st | Whole days from the start date to the next 1st of a month; 0 when the start date is the 1st. |
| date | Next 1st | The first date on or after the start date that is the 1st of its month. |
| after | The 1st after | The next 1st after that date. |

## Method

Find the first date on or after the start date that is the 1st of its month, then count the days from the start date to it.

## Assumptions

- On the 1st, the count is 0, and the 1st after is the 1st of the next month that has one.
- Every month has a 1st, so the next one is never more than a month away.
- The start date itself is not counted: from the day before, the count is 1.
- Dates are calendar days with no time of day, so a time zone or a daylight-saving change never adds or loses a day.
- Start dates from January 1, 1900 to December 31, 2400 work.

## Worked examples

1. from = 2026-10-19 gives date = 2026-11-01, days = 13, after = 2026-12-01. Source: IETF RFC 3339, section 5.7 (days in each month) and Appendix C (the leap year rule) (https://www.rfc-editor.org/rfc/rfc3339).
2. from = 2026-12-31 gives date = 2027-01-01, days = 1, after = 2027-02-01. Source: IETF RFC 3339, section 5.7 (days in each month) and Appendix C (the leap year rule) (https://www.rfc-editor.org/rfc/rfc3339).
3. from = 2027-02-01 gives date = 2027-02-01, days = 0, after = 2027-03-01. Source: IETF RFC 3339, section 5.7 (days in each month) and Appendix C (the leap year rule) (https://www.rfc-editor.org/rfc/rfc3339).
4. from = 2028-02-15 gives date = 2028-03-01, days = 15, after = 2028-04-01. Source: IETF RFC 3339, section 5.7 (days in each month) and Appendix C (the leap year rule) (https://www.rfc-editor.org/rfc/rfc3339).

## FAQ

### How many days until the 1st?

It depends on the date, so the count above starts from today as your device shows it. From the last day of a month, the next 1st is 1 day away; on the 1st itself the count is 0. Change “Count from” to count from another date.

### What if today is the 1st?

Then the count is 0, because the next 1st on or after today is today itself. The page also shows the 1st after it, which is 28 to 31 days later.

### Which months have a 1st?

All 12. Every month has at least 28 days, so every month has a 1st.

### How many times does the 1st come in a year?

12, one in every month.

### How many days until next month?

On any day but the 1st, it equals the days until the 1st, because next month starts on the next 1st. From the last day of a month the count is 1. On the 1st itself the count is 0. Next month then starts on the 1st after, which the page also shows: 28 to 31 days later.

### How are the days until the 1st counted?

From the start date (today, unless you change it) to the next 1st, without counting the start date, in calendar days. Weekends and holidays count like any other day.

## Sources

- IETF RFC 3339, Date and Time on the Internet: Timestamps, section 5.7 (the days in each month) and Appendix C (the leap year rule). https://www.rfc-editor.org/rfc/rfc3339
- U.S. Naval Observatory, Leap Years: the Gregorian leap year rule. https://aa.usno.navy.mil/faq/leap_years