How to specify a calculated value for a SharePoint custom field in its XML schema?
Like this:
<Field
Type="DateTime"
Format="DateOnly"
DisplayName="ExpiryDate"
Required="FALSE"
EnforceUniqueValues="FALSE"
Group="My Group"
ID="{99668BDC-5DED-46d0-A4EC-360237966F52}"
StaticName="ExpiryDate"
Name="ExpiryDate">
<DefaultFormula>[today]+60</DefaultFormula>
</Field>