TODAY

What it does

TODAY()

TODAY returns the current date as a whole date serial, with no time component. It reads the host's clock and takes no arguments.

Like NOW, it is not a function in the mathematical sense: it maps nothing to a value that changes. Three facts govern it, and they are the same three, with one difference that turns out to matter.

It is volatile

Here is the difference that matters: TODAY's value is constant for a day, so the volatility is almost always invisible. A TODAY-driven model recalculates constantly and produces the same answer, right up until midnight, when everything changes at once. That combination — expensive and silent, then abruptly different — is why TODAY in a large dependency tree is a well-known performance and reproducibility hazard.

The battery refuses it, correctly

This is worth stating plainly because TODAY looks so much more tractable than NOW — its value is stable for twenty-four hours, so a naive suite could "pass" for a day and then fail. Stability is not determinism.

It carries a formatting hint

TODAY is, with NOW, one of the documented seed examples for the presentation-hint model: the function returns a plain number and the host applies a date format when the formula is entered into a General-formatted cell. The value itself is core; the formatting is host-side adaptation at the worksheet boundary. See the value universe and the call pipeline, stage 4.

Arguments

TODAY() — no arguments. The parentheses are syntax; there is no parameter slot and therefore no Missing marker.

Everything that varies about the result comes from outside the call: the machine's clock and time zone, and the workbook's date system.

Try it

Quirks

Result and edge cases

Returns a Number: a whole date serial, with the fractional part zero.

• Local date, not UTC. The same workbook opened in two time zones can show two different dates for several hours each day.
• Midnight is a discontinuity, and it is the only interesting moment in the function's behaviour. A recalculation that spans it, or two cells evaluated either side of it, can disagree.
• Whole-day exactness. Because the result is an integer-valued double, TODAY() is safe for equality comparison against other whole serials in a way NOW is not. This is the practical reason to prefer TODAY whenever the time of day is not wanted: A1 = TODAY() works, A1 = NOW() almost never does.
• A static date is not this function. Excel's shortcut for entering today's date inserts a literal serial; it looks identical in the cell and never changes.

Errors

TODAY takes no arguments and has no documented error return. Its failure modes are host-level — an unavailable clock, or a system date outside the representable serial range — and are not observable as worksheet error values.

How to implement

Notes for implementers

1. Inject the clock. A time provider supplied through the execution context is what makes everything around this function testable, even though the function is not. The reference engine declares exactly such a dependency.
2. Derive TODAY from the same instant as NOW within a recalculation pass. If the two read the clock independently, a pass that spans midnight can produce a TODAY and a NOW that disagree about the date — an inconsistency no formula author can defend against.
3. Truncate, do not round. TODAY is the whole-day part of the current instant; rounding would make it flip at noon.
4. Declare volatility so the recalculation engine propagates it.
5. Record the time zone with any captured observation. A logged TODAY value without its zone is ambiguous for several hours a day.

Rust code

25 today_fn "TODAY" (0, 0) [] |s, a, sv| {
    let now = now(s)?;
    serial_out(s, Ok(now.floor()))
}

No implementation has been published with a Handbook test suite for this function.

Version differences

No comparison between specific Excel builds is recorded here yet. This does not establish that all builds behave alike.

Alternatives

Relationships

• NOW — the instant-reading sibling. TODAY() is expected to equal INT(NOW()); unverified here and interesting exactly at midnight.
• DATEDIF — DATEDIF(birthdate, TODAY(), "Y") is the canonical age formula, and the reason TODAY's volatility is tolerated in so many workbooks.
• DATEVALUE — shares an under-appreciated property: its documented year-omitted rule reads the system clock, making it clock-dependent too, though it is not declared volatile. TODAY is honest about depending on the clock; DATEVALUE is not.
• DATE — the deterministic constructor. Any formula that can name its date explicitly should, because it then becomes reproducible and testable.
• Volatile peers — NOW, RAND, RANDBETWEEN, OFFSET, INDIRECT, CELL, INFO.

Named variants

No named variants are recorded yet.