Reference · Dates

date.add_days

date.add_days(str, int) -> str

What it does

A date some days later, or earlier with a negative count, as ISO text. Months, years and leap days are crossed as the calendar has them. It takes a date, not a date-time: get a date-time's date with date.date_in first.

Examples

print(date.add_days("2026-10-27", 7), date.add_days("2026-10-27", -27))print(date.add_days("2026-12-31", 1), date.add_days("2024-02-28", 1))

2026-11-03 2026-09-302027-01-01 2024-02-29

Edge cases

• Zero gives the date itself.
• A float with a whole value is taken as an int.
• The result stays within years 1 to 9999: past the end it is a runtime error, as is a count beyond four million days either way.

print(date.add_days("2026-10-27", 0), date.add_days("2023-02-28", 1.0))print(date.add_days("0001-01-01", 3652058))

2026-10-27 2023-03-019999-12-31

Errors

A date-time, text that is not a date, a count that is not an int, or a result out of range is a runtime error, not an error value.

print(date.add_days("2026-10-27T10:00:00Z", 1))

line 1: `date.add_days` expects a date (YYYY-MM-DD) as argument 1, got the date-time "2026-10-27T10:00:00Z" (`date.date_in` gives its date)

print(date.add_days("9999-12-31", 1))

line 1: `date.add_days`: the date is out of range (years 1 to 9999)

Chaining

The date comes first in a pipeline:

print("2026-10-27" | date.add_days(14) | date.format("ddd D MMM"))print(range(0, 3) | map((i) => "2026-10-30" | date.add_days(i)))

Tue 10 Nov["2026-10-30", "2026-10-31", "2026-11-01"]

See also

date.add_months, date.add_years, date.days_between, date.date_in, date.today

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