The top of the chart
The Midheaven is the point where the ecliptic crosses your local meridian, the imaginary line running overhead from due north to due south. In a chart wheel it is the line pointing straight up, usually labeled MC, from the Latin medium coeli, meaning the middle of the sky.
Do not confuse it with the point directly overhead. The MC is where the zodiac reaches its highest point along the meridian, which is often well to the south of straight up for US birthplaces.
What astrologers read in the MC
The Midheaven is traditionally linked with public life, reputation, career direction and the role a person wants to be known for. If the Ascendant is read as how you meet people one on one, the MC is read as how you are seen by the wider world.
Its opposite point, the IC at the bottom of the chart, is linked with home, roots and private life. Together the MC and IC form the vertical axis of the chart, balancing the horizontal axis of the Ascendant and Descendant.
Time sensitivity, and why the MC is a bit steadier
Like the Ascendant, the Midheaven turns with the Earth and passes through all twelve signs in about a day, so an exact birth time is essential. Its speed is more even than the rising sign's, because it depends on the meridian rather than on how steeply each sign meets the horizon.
Even so, a gap of 15 to 20 minutes can move the MC several degrees. If your Midheaven sits near the edge of a sign, a more precise birth time may change the result.
How the calculator gets there
We look up the latitude, longitude and historical time zone of your birthplace, convert your local time to UTC and compute local sidereal time with Astronomy Engine. From that we find the zodiac degree on your meridian.
In the Placidus and most other quadrant house systems, the MC is also the cusp of the tenth house. In Whole Sign houses it can fall in the ninth, tenth or eleventh house, which some astrologers read as an extra layer of meaning.
Pair the MC with other angles
Your Midheaven makes the most sense alongside your Ascendant, so try the rising sign calculator next. The planet ruling your MC sign is often read for clues about public goals.
To see all four angles on a wheel, open your birth chart. The house calculator lists every house cusp, the tenth included.