Under New Hampshire law, a court may modify an existing parenting plan if there has been a substantial change in circumstances that affects the welfare of the child. This is set forth in RSA 461-A:11, which is the statute that governs parenting plans in New Hampshire.

The statute does not define what constitutes a substantial change in circumstances, but courts have interpreted it to mean a change that is significant and ongoing, not merely temporary or minor. Examples of circumstances that might warrant a modification of a parenting plan include:

Relocation: One parent has moved to a different city or state, making the existing parenting plan unworkable.
Parental availability: One parent’s work schedule has changed, making it difficult for them to comply with the existing parenting plan.

Child’s needs: The child’s medical or educational needs have changed, requiring a modification of the parenting plan.

Child’s age: As the child grows older, their needs and preferences may change, necessitating a modification of the parenting plan.

Safety concerns: One parent has become unfit to care for the child due to substance abuse, domestic violence, or other factors that pose a risk to the child’s safety.
The complete statute is set forth below:

461-A:11 Modification of Parental Rights and Responsibilities. –

I. The court may issue an order modifying a permanent order concerning parental rights and responsibilities under any of the following circumstances:

(a) The parties agree to a modification.

(b) If the court finds repeated, intentional, and unwarranted interference by a parent with the residential responsibilities of the other parent, the court may order a change in the parental rights and responsibilities without the necessity of showing harm to the child, if the court determines that such change would be in accordance with the best interests of the child.

(c) If the court finds by clear and convincing evidence that the child’s present environment is detrimental to the child’s physical, mental, or emotional health, and the advantage to the child of modifying the order outweighs the harm likely to be caused by a change in environment.

(d) If the parties have substantially equal periods of residential responsibility for the child and either each asserts or the court finds that the original allocation of parental rights and responsibilities is not working, the court may order a change in allocation of parental rights and responsibilities based on a finding that the change is in the best interests of the child.

(e) If the court finds by clear and convincing evidence that a minor child is of sufficient maturity to make a sound judgment, the court may give substantial weight to the preference of the mature minor child as to the parent with whom he or she wants to live. Under these circumstances, the court shall also give due consideration to other factors which may have affected the minor child’s preference, including whether the minor child’s preference was based on undesirable or improper influences.
(f) The modification makes either a minimal change or no change in the allocation of parenting time between the parents, and the court determines that such change would be in the best interests of the child.
(g) If one parent’s allocation of parenting time was based in whole or in part on the travel time between the parents’ residences at the time of the order and the parents are now living either closer to each other or further from each other by such distance that the existing order is not in the child’s best interest.
(h) If one parent’s allocation or schedule of parenting time was based in whole or in part on his or her work schedule and there has been a substantial change in that work schedule such that the existing order is not in the child’s best interest.

(i) If one parent’s allocation or schedule of parenting time was based in whole or in part on the young age of the child, the court may modify the allocation or schedule or both based on a finding that the change is in the best interests of the child, provided that the request is at least 5 years after the prior order.
II. Except as provided in RSA 461-A:11, I(b)-(f) for parenting schedules and RSA 461-A:12 for a request to relocate the residence of a child, the court may issue an order modifying any section of a permanent parenting plan based on the best interest of the child. RSA 461-A:5, III shall apply to any request to modify decision-making responsibility.

II. Except as provided in RSA 461-A:11, I(b)-(i) for parenting schedules and RSA 461-A:12 for a request to relocate the residence of a child, the court may issue an order modifying any section of a permanent parenting plan based on the best interest of the child. RSA 461-A:5, III shall apply to any request to modify decision-making responsibility.
III. For the purposes of this section, the burden of proof shall be on the moving party.

It’s important to note that the change in circumstances must affect the child’s welfare, not just the parents’ convenience. Additionally, the parent seeking the modification has the burden of proving that a modification is necessary and in the best interests of the child.