Genealogical rules of thumb

According to Wikipedia a rule of thumb is a principle with broad application that is not intended to be strictly accurate or reliable for every situation. It is an easily learned and easily applied procedure for approximately calculating or recalling some value, or for making some determination.

Here are a few rules of thumb in genealogy.

1. A women will typically first marry at age 21, so if you have a year of marriage subtract 21 for a rule of thumb estimate of the birth year. Add 21 to the year of birth for the marriage year.

2. A man will often be a year or two older than his wife, say age 23, at marriage.

3. The first child will typically be born 1 - 2 years after marriage.

4. If there are many children in a family they will typically be born a couple of years apart. If there is a gap it may indicate a miscarriage or unrecorded still birth. It may also signal a child who died young and born while the family was temporarily relocated.

5. The average span of a generation, between the birth of a parent and a child, is 25 - 30 years.