Monthly Gantt Chart

{
  "$schema": "https://developer.microsoft.com/json-schemas/sp/v2/column-formatting.schema.json",
  "elmType": "div",
  "style": {
    "display": "=if([$StartDate],'flex','none')",
    "flex-direction": "column",
    "width": "200px",
    "height": "75px",
    "margin": "5px"
  },
  "children": [
    {
      "elmType": "span",
      "style": {
        "width": "100%",
        "text-align": "center",
        "font-weight": "bolder"
      },
      "txtContent": "=if(getMonth([$StartDate])=='','', [$StartDate.displayValue]+' - '+ [$EndDate.displayValue])",
      "attributes": {
        "class": "ms-fontColor-themePrimary"
      }
    },
    {
      "elmType": "div",
      "style": {
        "display": "flex",
        "justify-content": "space-between",
        "width": "100%",
        "padding-bottom": "5px",
        "margin-left": "-5px"
      },
      "attributes": {
        "class": "ms-fontColor-themePrimary ms-fontWeight-bold"
      },
      "children": [
        {
          "elmType": "span",
          "txtContent": "1"
        },
        {
          "elmType": "span",
          "txtContent": "5"
        },
        {
          "elmType": "span",
          "txtContent": "10"
        },
        {
          "elmType": "span",
          "txtContent": "15"
        },
        {
          "elmType": "span",
          "txtContent": "20"
        },
        {
          "elmType": "span",
          "txtContent": "25"
        },
        {
          "elmType": "span",
          "txtContent": "30"
        }
      ]
    },
    {
      "elmType": "div",
      "style": {
        "width": "100%",
        "border": "2px solid",
        "height": "30px",
        "fill": "currentColor"
      },
      "attributes": {
        "class": "ms-fontColor-themePrimary"
      },
      "children": [
        {
          "elmType": "svg",
          "style": {
            "width": "100%",
            "height": "100%",
            "display": "=if([$EndDate]>=[$StartDate],'','none')"
          },
          "children": [
            {
              "elmType": "path",
              "attributes": {
                "d": "= 'M ' + ((Number(Date([$StartDate]))/1000/60/60/24)-(Number(Date(''+ (getMonth([$StartDate]) + 1) + '/1/' + getYear([$StartDate]) ))/1000/60/60/24))*6.452 + ',0  ' + ((Number(Date([$EndDate]))/1000/60/60/24)-(Number(Date(''+ (getMonth([$StartDate]) + 1) + '/1/' + getYear([$StartDate]) ))/1000/60/60/24)+1)*6.452 + ',0 ' + ((Number(Date([$EndDate]))/1000/60/60/24)-(Number(Date(''+ (getMonth([$StartDate]) + 1) + '/1/' + getYear([$StartDate]) ))/1000/60/60/24)+1)*6.452 + ',40 ' + ((Number(Date([$StartDate]))/1000/60/60/24)-(Number(Date(''+ (getMonth([$StartDate]) + 1) + '/1/' + getYear([$StartDate]) ))/1000/60/60/24))*6.452 + ', 40 Z'"
              }
            }
          ]
        }
      ]
    }
  ]
}