There is more than one way to cut the sky into twelve. We default to Porphyry.
Because houses are a convention rather than an observation, astrologers have never agreed on how to draw the dividing lines. Dozens of systems exist. They agree on the Ascendant and the Midheaven (those are astronomy) and disagree about everything in between.
Porphyry, the default here
Take the Ascendant as the first cusp and the Midheaven as the tenth. That plus their opposite points gives four quadrants. Divide each quadrant into three equal parts. Done. Porphyry is chosen here because it treats the four angles as the load-bearing structure of the chart, which is what most people find they respond to, and because the arithmetic is honest about being a convention rather than dressing it up.
Whole Sign, the oldest
The entire sign containing your Ascendant becomes the first house, the next sign the second, and so on. Every house is exactly 30°, and house boundaries and sign boundaries are the same lines. It is the original system, it is the easiest to hold in your head, and it cannot produce the strange edge cases the quadrant systems can.
Placidus, the most common
A time-based method from the Renaissance: cusps are marked by how long each degree of the ecliptic takes to climb from the horizon to the meridian. It produces houses of markedly unequal size, and the further you were born from the equator, the more unequal they get. Beyond the polar circles it breaks down completely, because some degrees of the zodiac never touch the horizon there at all.