In most cases the court can only change support for installments that come due after you file your motion. Colorado law says child support and maintenance orders are modifiable only as to installments accruing after the motion is filed. The judge typically makes the new amount effective as of the filing date unless doing so would cause hardship or substantial injustice. The statute also explains how support becomes a judgment if unpaid and how it can be enforced. Limited retroactivity can apply when the parties mutually agreed to change physical care and later seek to update support. Ask your lawyer to file promptly so any change can take effect without delay.