Concept
Daylight saving time: the one-hour error hiding in birth records
DST moves the clock, not the sun. A birth recorded at 12:30 in July may be 11:30 by the sun's reckoning before any other correction is applied.
Why DST is the largest single correction
Longitude offsets are usually under half an hour and the equation of time under sixteen minutes — but DST is a full hour, applied or not applied as a step function. It is also the easiest to get wrong from memory, because rules varied by year, region, and even wartime emergency decrees. We resolve it from the IANA tz database for your exact birth date and place, and show the result as its own line in the correction breakdown.
Order of operations
The engine first converts recorded clock time to standard time (undoing DST if it applied), then applies the longitude correction, then the equation of time. Each step is displayed separately in your chart’s true-solar-time panel, so a skeptical reader can verify every minute of the total adjustment.
When two tools show different hour or day pillars, use the calculator-disagreement audit to compare the historical offset before comparing their interpretations. A tool using today’s offset for an older birth can diverge before longitude or solar time is even considered.
Questions
Frequently asked
You usually don't have to — the IANA timezone database records historical DST rules for each region, and our calculator applies them automatically from your birthplace and date.
Rules changed often: many countries adopted, dropped and re-adopted DST across the 20th century, including wartime double summer time in parts of Europe. This is exactly why a database lookup beats memory.
Rarely — a one-hour shift can also move a birth across midnight or, at the extreme, across a solar-term boundary near the month change, which is why we correct time before deriving any pillar.
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