How much of the sign is left
At noon in every year from 1930 to 2035 the Sun on 17 April stood between roughly twenty six and a half and twenty eight degrees of Aries. The sign ends at thirty. The Sun covers about a degree a day, so a birth on this date is around three days short of the Taurus boundary.
Three days is a wide margin by the standards of this question. The boundary itself drifts by up to a day and a half depending on the year and the birth hour, and a margin of three days swallows that entirely. No plausible combination of year, hour and time zone makes 17 April anything other than Aries.
Late degrees and edge degrees are different things
A birth two hours from a sign change is genuinely undetermined until the year, the hour and the place are known. A birth three days from one is settled, and the correct response to it is not caution about the sign but interest in the degree.
The two get conflated because both are described as late in the sign. Only one of them is a question about which sign applies. This one is not, and a reader on this date can take Aries as given and move on to the layers underneath it.
The practical test is simple. Ask how many days of solar motion lie between the position and the boundary, since the Sun moves about a degree a day. Under a day and the answer needs the birth hour, a day or two and it needs the year, and beyond that the sign holds however the details fall. On 17 April the gap is comfortably in the last category.
What the older material says about closing degrees
Twenty seven degrees falls in the third face of Aries, from twenty to thirty, which the Chaldean order gives to Venus and the triplicity scheme gives to Jupiter. Marked as tradition rather than fact, the closing degrees of a sign were read as the sign at its most developed and most nearly finished, with the following sign not yet in play.
Some sources go further and treat the last degrees as weak or unstable. That reading belongs to a specific technical context about planets applying to a boundary, and it does not transfer to a Sun sitting comfortably inside the sign. A Sun at twenty seven degrees of Aries is as much in Aries as one at fifteen.
The rest of the chart, which the date does not touch
The Moon on 17 April can be in either of two signs depending on the hour, and in any of the twelve across different years. The ascendant changes about every two hours and depends on latitude as well as clock time, so the date cannot reach it and neither can a guess.
What the date gives is one clear placement: a Sun in the closing third of a cardinal fire sign ruled by Mars, near twenty seven degrees. The widget above takes your year, hour and birthplace and replaces that range with your exact figure, along with how far you were born from the nearest sign boundary.
Questions people ask about this
Is 17 April Aries or Taurus?
Aries, without exception in the sampled century. The Sun is around three days from the Taurus boundary on this date, which is far more margin than the year to year drift can cover.
Am I on the Aries Taurus cusp?
No. A cusp describes a birth close enough to a boundary that the sign is genuinely in doubt, and three days is not close. There is no blended condition to be in.
Does being late in Aries weaken the placement?
Not in any technical sense that applies here. The idea comes from a narrower rule about planets approaching a boundary, and it is not a statement about a Sun sitting three days inside its sign.
What degree is a 17 April Sun?
Close to twenty seven degrees of Aries, with a century range of about twenty six and a half to twenty eight. The widget above gives your exact figure from your own year, hour and place.
Which decan is that?
The third decan of Aries, twenty to thirty degrees, ruled by Venus in the Chaldean count and by Jupiter in the triplicity count.
When does Aries actually end?
Around 19 or 20 April, at the moment the Sun reaches thirty degrees of ecliptic longitude. The exact instant moves by up to a day and a half between years and depends on your time zone.