You can calculate interest yourself if you have the talent in that department. An attorney can do likewise. There are programs for calculating arrearage interest, but some are not very good and unless you have only one judgment date, calculating child support intrest can get complicated.
The state usually does not calculate interest. It is just too complicated for not really much money but you can insist they do it.
Yes you must ask for the interest. You can try to calculate it yourself by using an online program or enlist the services of a private attorney.
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