Many single parent families are already under huge pressure. Many are self-employed so as to be more flexible for their children. The MIF assumes a certain level of income earned no matter the actual income and ability to work based on current circumstances. It is flawed for so many reasons.
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To earn the amount assumed by the minimum income floor as a single parent family can be nigh on impossible. If a child/parent becomes unwell, the parent cannot work so the family suffers financially. If a child has additional needs and is awaiting assessment (which can take years), or the parent has no transport of their own, or cannot find suitable childcare nearby for holiday periods, or has no help from family or the other parent, this is not accounted for by UC.