How to: Create a Calendar Heatmap

Steps to create:
Select a chart you want to replace the calendar heatmap with and go to the code view
Select the Date Column and the metric you want to display
Paste the following code, replace the dateColumn, metricColumn and metricPrefix to the date and metric column you selected. If the metric is not a currency, change the metricPrefix to remove the dollar sign:
JS
function CalendarHeatmapByDay({ data = [] }) {

  const dateColumn = 'date';
  const metricColumn = 'cost';
  const metricPrefix = '$';

  const byDate = new Map();
  const yearsSet = new Set();

  data.forEach(item => {
    if (!item[dateColumn]) return;
    const [mm, dd, yyyy] = item[dateColumn].split("/").map(s => s.padStart(2, "0"));
    const iso = `${yyyy}-${mm}-${dd}`;
    yearsSet.add(yyyy);
    const v = Number(item[metricColumn]) || 0;
    byDate.set(iso, (byDate.get(iso) || 0) + v);
  });

  const years = [...yearsSet].sort((a, b) => Number(a) - Number(b));
  const monthNames = ["Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"];

  const maxCost = byDate.size === 0 ? 0 : Math.max(...byDate.values());
  const GREENS = [
    "#e5f5e0", "#c7e9c0", "#a1d99b", "#74c476", "#41ab5d",
    "#238b45", "#006d2c", "#00441b"
  ];

  const costs = Array.from(byDate.values()).filter(v => v > 0).sort((a, b) => a - b);
  const median = costs.length ? (costs[Math.floor((costs.length - 1) / 2)] + costs[Math.ceil((costs.length - 1) / 2)]) / 2 : 0;
  const absDevs = costs.map(v => Math.abs(v - median)).sort((a, b) => a - b);
  const mad = absDevs.length ? (absDevs[Math.floor((absDevs.length - 1) / 2)] + absDevs[Math.ceil((absDevs.length - 1) / 2)]) / 2 : 0;
  let scale = mad * 1.4826;
  if (!scale) {
    const min = costs.length ? costs[0] : 0;
    const max = costs.length ? costs[costs.length - 1] : 0;
    scale = (max - min) / 6 || 1;
  }
  const clamp = (x, lo, hi) => Math.max(lo, Math.min(hi, x));

  const colorFor = cost => {
    if (cost <= 0 || !isFinite(cost)) return "#f0f0f0";
    const z = (cost - median) / scale;
    const zClamped = clamp(z, -2.5, 2.5);
    const t = (zClamped + 2.5) / 5;
    const idx = Math.round(t * (GREENS.length - 1));
    return GREENS[idx];
  };

  const daysInMonth = (y, m) => new Date(y, m + 1, 0).getDate();
  const firstDow = (y, m) => new Date(y, m, 1).getDay();
  const weeksInMonth = (y, m) => Math.ceil((firstDow(y, m) + daysInMonth(y, m)) / 7);

  const baseLabelCol = 18;
  const dim = 18;
  const dayGap = 4;
  var showWeekdayLabels = true;

  const showTooltip = (e, text) => {
    const tooltip = document.createElement('div');
    tooltip.style.position = 'fixed';
    tooltip.style.background = 'rgba(0,0,0,0.75)';
    tooltip.style.color = '#fff';
    tooltip.style.padding = '3px 6px';
    tooltip.style.borderRadius = '3px';
    tooltip.style.fontSize = '11px';
    tooltip.style.pointerEvents = 'none';
    tooltip.style.zIndex = '1000';
    tooltip.innerHTML = text;
    document.body.appendChild(tooltip);

    const rect = e.target.getBoundingClientRect();
    tooltip.style.top = `${rect.top - tooltip.offsetHeight - 4}px`;
    tooltip.style.left = `${rect.left + rect.width / 2 - tooltip.offsetWidth / 2}px`;
    e.target._tooltip = tooltip;
  };

  const hideTooltip = (e) => {
    if (e.target._tooltip) {
      document.body.removeChild(e.target._tooltip);
      e.target._tooltip = null;
    }
  };

  return React.createElement("div", { style: { padding: 12 } },
    React.createElement("div", { style: { marginBottom: 8, fontSize: 16, fontWeight: 700 } }, "Media Spend by Day"),
    years.length === 0
      ? React.createElement("div", { style: { color: "#666" } }, "No data.")
      : years.map(yyyy =>
        React.createElement("div", { key: yyyy, style: { marginBottom: 12 } },
          React.createElement("div", { style: { fontWeight: 700, fontSize: 14, marginBottom: 4 } }, yyyy),
          React.createElement("div", {
            style: {
              display: "grid",
              gridTemplateColumns: "repeat(auto-fill, 160px)",
              justifyContent: "start",
              gap: 8, // month gap
              alignItems: "start",
              gridAutoFlow: "row dense"
            }
          },
            Array.from({ length: 12 }).map((_, mIndex0) => {
              const monthLabel = monthNames[mIndex0];
              const weeks = weeksInMonth(Number(yyyy), mIndex0);
              const firstDay = firstDow(Number(yyyy), mIndex0);

              const tiles = [];
              const totalDays = daysInMonth(Number(yyyy), mIndex0);
              let hasData = false;

              const labelCol = showWeekdayLabels ? baseLabelCol : 0;
              const tileColStart = showWeekdayLabels ? 2 : 1;

              for (let d = 1; d <= totalDays; d++) {
                const dt = new Date(Number(yyyy), mIndex0, d);
                const dow = dt.getDay();
                const week = Math.floor((firstDay + (d - 1)) / 7);
                const mm = String(mIndex0 + 1).padStart(2, "0");
                const dd = String(d).padStart(2, "0");
                const iso = `${yyyy}-${mm}-${dd}`;
                const cost = byDate.get(iso) || 0;
                if (cost > 0) hasData = true;

                tiles.push(
                  React.createElement("div", {
                    key: iso,
                    style: {
                      gridRow: dow + 2,
                      gridColumn: week + tileColStart,
                      width: dim,
                      height: dim,
                      borderRadius: 3,
                      background: colorFor(cost),
                      cursor: cost > 0 ? "pointer" : "default"
                    },
                    onMouseEnter: (e) => showTooltip(e, `${monthLabel} ${d}, ${yyyy} — ${metricPrefix}${cost.toLocaleString(undefined, { minimumFractionDigits: 2, maximumFractionDigits: 2 })}`),
                    onMouseLeave: hideTooltip
                  })
                );
              }

              if (!hasData) return null;

              const weekdayLabels = showWeekdayLabels
                ? ["S", "M", "T", "W", "T", "F", "S"].map((lbl, i) =>
                  React.createElement("div", {
                    key: lbl,
                    style: {
                      gridRow: i + 2,
                      gridColumn: 1,
                      width: baseLabelCol,
                      textAlign: "right",
                      paddingRight: 2,
                      fontSize: 9,
                      color: "#888",
                      alignSelf: "center",
                      justifySelf: "end",
                      lineHeight: `${dim}px`
                    }
                  }, lbl)
                )
                : [];
              showWeekdayLabels = false;
              return React.createElement("div", {
                key: `${yyyy}-${mIndex0}`,
                style: {
                  maxWidth: "160px",
                  borderRadius: 8,
                  padding: 4,
                  background: "#fff"
                }
              },
                React.createElement("div", {
                  style: { fontWeight: 600, fontSize: 12, marginBottom: 4, textAlign: "center" }
                }, monthLabel),
                React.createElement("div", {
                  style: {
                    display: "grid",
                    gridTemplateColumns: `${showWeekdayLabels ? baseLabelCol + 'px ' : ''}repeat(${weeks}, ${dim}px)`,
                    gridTemplateRows: `12px repeat(7, ${dim}px)`,
                    gap: dayGap,
                    alignItems: "center",
                    justifyContent: "start"
                  }
                },
                  showWeekdayLabels ? React.createElement("div", { style: { gridRow: 1, gridColumn: 1 } }) : null,
                  ...Array.from({ length: weeks }).map((_, w) =>
                    React.createElement("div", {
                      key: `w-${w}`,
                      style: {
                        gridRow: 1,
                        gridColumn: w + tileColStart,
                        fontSize: 9,
                        color: "#aaa",
                        justifySelf: "center"
                      }
                    })
                  ),
                  ...weekdayLabels,
                  ...tiles
                )
              );
            })
          )
        )
      ),
    React.createElement("div", { style: { display: "flex", alignItems: "center", gap: 4, marginTop: 6 } },
      React.createElement("span", { style: { fontSize: 11, color: "#666" } }, "Less"),
      ...GREENS.map((c, i) =>
        React.createElement("div", { key: i, style: { width: 12, height: 12, borderRadius: 3, background: c } })
      ),
      React.createElement("span", { style: { fontSize: 11, color: "#666" } }, "More")
    )
  );
}