Hello Aidan,

Thank you for posting in our community.

By design the igFiltering input editors will take the format set for the corresponding column. What I can suggest is setting this property for the date column and this automatically use the same formatting for the editors. For example:

 $("#grid1").igGrid({
             autoGenerateColumns: false,
             autoCommit: true,
             columns: [
                    { headerText: "Product ID", key: "ProductID", dataType: "number", width: "200px" },
                    { headerText: "Product Name", key: "Name", dataType: "string", width: "200px" },
                    { headerText: "Product Number", key: "ProductNumber", dataType: "string", width: "200px" },
                    { headerText: "Standard Cost", key: "StandardCost", dataType: "number", width: "200px" },
                    { headerText: "Make flag", key: "MakeFlag", dataType: "bool", width: "200px" },
                    { headerText: "Sell Start Date", key: "SellStartDate", dataType: "date", width: "200px", format: "dd-MM-yy" }
             ],
             primaryKey: "ProductID",
             dataSource: adventureWorks,
             renderCheckboxes: true,
             features: [
                    {
                        name: 'Filtering',
                        mode : "advanced"
                    }]
         });

I also made a small sample illustrating my suggestion and I am attaching it for your reference.

Please have a look at the sample and if you have any additional questions afterwards please feel free to contact me.