23 July to 22 August
The season runs from a hundred and twenty degrees of ecliptic longitude to a hundred and fifty, which in current years means 22 or 23 July to 22 or 23 August. Every figure in that sentence except the degrees is approximate, and the degrees are the definition.
The dates move because the calendar cannot represent a tropical year exactly. Six hours or so of surplus each year push both ingresses later; the extra day in February pulls them back; the pattern repeats on a four year cycle without accumulating.
The Sun in the sign it rules
Leo is the only season the Sun spends in its own domicile, so its rulership and its actual position coincide for this month and for no other. It is a fixed sign, seated in the middle of the northern summer rather than at a turning point, and the Sun's declination falls steadily throughout it after the June extreme.
Leo has no traditional exaltation, which it shares with only a couple of other signs. Its decans go to Saturn, Jupiter and Mars in ten degree bands, so the sign most associated with the Sun is governed in detail by three planets that are not the Sun.
Sidereal Leo starts in the middle of August
The Indian systems measure from the fixed stars. Since the equinox slides backwards against those stars, currently by about twenty four degrees of accumulated drift, every sidereal boundary sits later in the calendar than its Western counterpart by a little over three weeks.
That puts sidereal Leo from around mid August to mid September. Someone born in the first three quarters of the Western range has a sidereal Sun in Cancer, and neither reading is a mistake: the frames simply begin their count in different places.
Beyond the sun sign
Births within a couple of days of either edge cannot be decided from a table. The calculation needs the year, the clock time and the place, and it returns a longitude that is on one side of the boundary or the other with nothing in between.
The rest of a chart is out of a date's reach entirely. The Moon changes sign every couple of days, the Ascendant turns through the whole zodiac daily and depends on latitude, and the planets are where the year puts them rather than where the month does.
Questions people ask about this
What are the Leo dates?
Approximately 23 July to 22 August. The exact start falls on 22 or 23 July and the end on 22 or 23 August, varying with the year and with the time zone the birth is dated in.
Why do the dates change from year to year?
Because the tropical year is not a whole number of days. The ingress slips about six hours later each year and is pulled back by each leap day, so it oscillates across roughly a day and a half.
When is Leo season this year?
Within the range above, at a minute that has to be calculated for the specific year. Anyone born close to either edge needs the actual solar position rather than a table.
Why does Vedic astrology not make me Leo?
It measures from the fixed stars rather than from the equinox, and the two references have separated by about twenty four degrees. That moves every sidereal boundary later by a little over three weeks.
Does being born on the first day of Leo mean anything special?
It puts the Sun in the first degree of the sign, which matters for aspects and house placement. The tradition does not read it as a weaker or stronger version of the sign itself.