What is the day-for-a-year rule?

Secondary progression takes the chart for the nth day after birth and reads it for the nth year of life. Every progressed position on this page follows from that one substitution.

How often does a progressed Sun change sign?

About every thirty years, because it moves roughly a degree a year. Most people see two such changes.

How long is a progressed Moon cycle?

Twenty-seven to twenty-eight years for a full circuit, moving about one sign every two and a half years.

Progressions

Your chart, moved forward a day for every year

Secondary progressions are the oldest way astrology talks about change over a life, and the rule behind them is strange enough to state plainly: take the sky one day after you were born, and read it as your first year. Two days for your second. If you are thirty, your progressed chart is the sky thirty days after your birth. Nobody claims this is physical. It is a symbolic clock, and it moves slowly enough to be about chapters rather than days.

Why the Sun matters most here

Your progressed Sun moves about one degree a year, so it changes sign roughly every thirty. People often report those crossings as the years their priorities shifted, and whether that is the progression or simply what thirty years does to anyone is not something a chart can settle. The progressed Moon is the fast hand, about two and a half years to a sign, and the progressed lunation phase is the cycle the two make together over about twenty-nine and a half years.

What this calculation assumes

version: asternym-western-advanced-v1
zodiac: Tropical
progressionMethod: Secondary progressions: one day after birth stands for one year of life
requiresBirthTime: Solar returns and progressed angles need an exact birth time; without one they are withheld rather than estimated

How fast each progressed point actually moves

Secondary progression runs on one ratio: a day after birth stands for a year of life. That single rule sets every speed on the page, and the speeds are what make the technique readable, because they differ by an order of magnitude.

The progressed Sun moves roughly one degree a year, so it crosses a whole sign in about thirty. Most people get two of those changes in a lifetime, three if they are lucky with where their Sun started, and astrologers treat them as the slowest markers in the system. The progressed Moon is the fast one: about a sign every two and a half years, and a full circuit of the chart in twenty-seven to twenty-eight. If you have heard someone talk about a progressed Moon return, that is the age they mean.

Mercury, Venus and Mars progress at rates that depend on whether they were moving direct or retrograde around your birth, which is why two people born a fortnight apart can have progressed Venus positions that diverge sharply by their forties. The outer planets barely move at all under progression. Three degrees in eighty years is not a timing technique, which is why nobody reads progressed Neptune for anything.