Assuming for the sake of this answer that child support in your specific case would be governed under VA law, then the amount of support produced under the guidelines set forth in Va. Code Section 20-108.2 is presumed to be the correct amount of child support. The court may deviate from the guidelines in certain circumstances, but first determine the correct amount of support due under the VA guidelines calculations, state what that presumptively correct amount of support is, and then specifically state on the record what exacty the reasons are that the court has deviated from that amount.
Another issue to consider is that both parents have a legal obligation to provide/contribute financial support to their children. So, if you voluntarily reduce your income (either because you reduce your hours, chose to change careers/occupations, or you are terminated from your job for cause), the court may (and usually will in such circumstances) impute income to you (usually equal to what you were making prior to changing your employment/income situation). If the court imputes income to you for which you would need to incur additional day care expenses, then the court is suppose to add those imaginary figures into the child support calculation as well.
If your voluntary change in income is the only material change since the most recent support order was entered, then the court may well dismiss your petition for modification of support. Alternatively, if the court imputes incvome to you and adds the daycare expenses back into the equation, the result may very well be no change in guideline support and so the petition will be denied.
If, on the otherhand, the NCP gets wind of these changes and decides to file for a reduction in child support (and does not request that income be imputed to you or otherwise argue voluntary under-employment), then the court may well grant the NCP's petition -- unless you can successfully argue to the court sufficient reasons why the court should upwardly deviate from the guidelines.
I would recommend that you consult with a family law attorney and have that attorney run the various guideline scenarios for you, as well as review the specific details of your case with you, so that you can get a more detailed set of answers to your question.
This response does not create an attorney-client relationship and is intended for general information purposes only.
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