A boundary is a place, not a verdict
Sign boundaries are usually presented as a switch. A date is either inside a range or outside it, and the answer comes back as a name. That framing hides the only continuous piece of information in the system, which is how far the Sun actually was from the nearest edge.
On the eighteenth of August the noon position across the last century has run from about twenty four point six to twenty six degrees of Leo. Virgo opens at thirty. So the gap to the next boundary is four to five and a half degrees, and the gap back to Cancer is around twenty five. The sign is not marginal in any sense, and there is no cusp to discuss.
What the distance is good for
Degrees matter in ordinary chart work in ways the sign name does not. Aspects are measured between longitudes and are counted as exact within a few degrees, so a Sun at twenty five degrees of Leo relates to points near twenty five degrees of other signs, not to Leo as a whole. House placement depends on the degree too, since houses have boundaries of their own that fall wherever the chart puts them.
A birthday page that stops at the sign leaves all of that on the table. It also cannot tell a reader whether their own case is a close one, which is the single question people with birthdays near a boundary actually want answered.
There is a further use for the number. Two charts can be compared degree by degree rather than sign by sign, which is the difference between saying that two people are both Leo and saying that one person's Sun sits within two degrees of another's Moon. The first statement covers a twelfth of the population; the second describes a specific relationship between two positions.
The band, which is closer to home
The nearer edge in practical terms is the decan line at twenty degrees, which this date passed several days ago. Leo's closing band runs from there to the Virgo boundary and belongs to Mars, a reading the Chaldean count and the triplicity scheme both produce by separate routes.
The tradition takes Leo as fixed fire under the Sun and this last band as its most combative stretch. That is inherited interpretation and should be read as such. The position itself is not: any ephemeris will return the same longitude for the same instant regardless of which school compiled it.
The distances that cannot be worked out from a date
The Moon changes sign every two days or so and moves between twelve and fifteen degrees in twenty four hours, which means it can be in either of two signs on this date, and its distance from its own nearest boundary is unknowable without the hour. The Ascendant is unconstrained entirely, since all twelve signs rise in a single day and the speed at which each one does so depends on latitude.
The widget above takes the year, the hour and the birthplace, returns the solar longitude to the degree, and states plainly how far the position stood from the nearest sign boundary. On a date like this one the answer is comfortable rather than close, which is itself worth knowing rather than assuming.
Questions people ask about this
Is 18 August close to Virgo?
Not in any meaningful sense. The Sun is around twenty five degrees of Leo and Virgo opens at thirty, so there are four or five days of solar motion still to go.
What decan is an 18 August birthday in?
The third decan of Leo, which begins at twenty degrees. The date's whole range across the last century falls inside it, so the band does not depend on the year.
What is the exact solar degree?
Between about twenty four point six and twenty six degrees at noon, depending on the year. The widget above gives a single figure once your hour and birthplace are entered.
Why does distance from a boundary matter?
Because aspects and house placements are measured in degrees rather than signs. The degree also settles whether a reader's own case is genuinely borderline, which a date range cannot.
Is there a Leo Virgo cusp on this date?
No, and there is no cusp on any date. The Sun occupies one longitude at any instant, and on the eighteenth of August that longitude is several degrees inside Leo.
Does the birth time change the sign here?
Not at all. Half a day of solar motion is under half a degree, which cannot move a position four degrees from the nearest boundary.