One day after birth symbolically stands for one year of life.
To see what you are like at forty, you look at the sky forty days after your birth. It is a symbolic rather than physical technique, and describes inner maturation more than events: the progressed Moon, changing sign every two and a half years, is the most used indicator. Unlike the solar return, it stays anchored to the birthplace.
How the progressed date is worked out
The arithmetic is simple: take your age in years, fractions included, and count forward the same number of days from the moment of birth. At thirty and a half you look at the sky thirty and a half days after you were born. To turn years into days the site uses the average length of the tropical year, about 365.24 days, and calculates a full chart for the birthplace.
The progressed chart is then read against the natal one: which natal houses the progressed planets occupy and which aspects they make to your natal planets. Because everything moves slowly in progressions, a progressed aspect can stay active for years and is read as a season rather than an episode.
What actually moves
In progressions the planets barely shift. The progressed Sun advances about one degree a year and changes sign roughly every thirty years. Mercury, Venus and Mars may change sign or direction over a lifetime. The fastest is the Moon, which goes round the zodiac in about twenty-seven years.
That is why many astrologers follow the progressed lunar phase: the angle between the progressed Moon and Sun, divided into eight phases of 45° following Dane Rudhyar's scheme. A full cycle lasts around thirty years and is read as a major chapter of life, from the seeding of the progressed new Moon to the letting go of the balsamic phase.
Frequently asked questions
What is the difference between progressions and transits?
Transits compare your chart with the real sky of today: they describe what arrives from outside, on precise dates. Progressions let the chart itself evolve by the rule of a day for a year, and traditionally describe how you change from within. Many astrologers use the two together: transits for specific periods, progressions for the background of personal growth.
What does it mean when your progressed Moon changes sign?
Traditionally it marks a change of inner climate: for around two and a half years your emotional needs, and what makes you feel at ease, take on the colour of the new sign. The natal house the progressed Moon moves into matters as well, since it shows the area of life where your emotional attention tends to settle for a few years.
Can you use progressions without a birth time?
Partly. The progressed planets' positions remain usable, with a caveat for the Moon: at birth it moves about half a degree an hour, and in progressions about a degree a month, so a few hours' uncertainty shifts its timings by a few months. The progressed Ascendant, Midheaven and houses depend on the time and, without a reliable one, should not be taken seriously.
See it in your own chart
Calculating your birth chart is free: wheel, planets, houses, aspects and a first reading. All you need is your date, time and place of birth.