Time & Dates
Days between two dates
Because both dates are day counts from the same epoch, the difference is the exact number of days between them.
The Formula
Days = JDN(reference) - JDN(birth)
Because both dates are day counts from the same epoch, the difference is the exact number of days between them.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| JDN birth | Birth day number | day | The Julian day number of the birth date. |
| JDN ref | Reference day number | day | The Julian day number of the reference date. |
What Each Symbol Means
JDN birthday
Birth day number
The Julian day number of the birth date.
JDN refday
Reference day number
The Julian day number of the reference date.
See It Worked With Real Numbers
A formula on its own does not tell you which number goes where. The how to calculate age from date of birth page applies this equation to a concrete case, shows every intermediate step, and names the mistakes that produce a wrong answer even when the algebra is right.
Where This Formula Appears
This equation is the working core of How To Calculate Age From Date Of Birth, filed under Everyday Life. Every number the guide produces comes from substituting into this one line.