diff --git a/addons/spreadsheet/static/src/helpers/constants.js b/addons/spreadsheet/static/src/helpers/constants.js
index 58ba8e634cb..476c8b992f8 100644
--- a/addons/spreadsheet/static/src/helpers/constants.js
+++ b/addons/spreadsheet/static/src/helpers/constants.js
@@ -5,11 +5,11 @@ import { _lt } from "@web/core/l10n/translation";
 export const DEFAULT_LINES_NUMBER = 20;
 
 export const FORMATS = {
-    day: { in: "DD MMM YYYY", out: "MM/DD/YYYY", display: "DD MMM YYYY", interval: "d" },
-    week: { in: "[W]W YYYY", out: "WW/YYYY", display: "[W]W YYYY", interval: "w" },
-    month: { in: "MMMM YYYY", out: "MM/YYYY", display: "MMMM YYYY", interval: "M" },
-    quarter: { in: "Q YYYY", out: "Q/YYYY", display: "[Q]Q YYYY", interval: "Q" },
-    year: { in: "YYYY", out: "YYYY", display: "YYYY", interval: "y" },
+    day: { out: "MM/DD/YYYY", display: "DD MMM YYYY", interval: "d" },
+    week: { out: "WW/YYYY", display: "[W]W YYYY", interval: "w" },
+    month: { out: "MM/YYYY", display: "MMMM YYYY", interval: "M" },
+    quarter: { out: "Q/YYYY", display: "[Q]Q YYYY", interval: "Q" },
+    year: { out: "YYYY", display: "YYYY", interval: "y" },
 };
 
 export const HEADER_STYLE = { fillColor: "#f2f2f2" };
diff --git a/addons/spreadsheet/static/src/pivot/pivot_model.js b/addons/spreadsheet/static/src/pivot/pivot_model.js
index b3f14077227..2e6d790d2d9 100644
--- a/addons/spreadsheet/static/src/pivot/pivot_model.js
+++ b/addons/spreadsheet/static/src/pivot/pivot_model.js
@@ -448,23 +448,38 @@ export class SpreadsheetPivotModel extends PivotModel {
      */
     _getGroupValues(group, groupBys) {
         return groupBys.map((groupBy) => {
-            return this._sanitizeValue(group[groupBy], groupBy);
+            const { field, aggregateOperator } = this.parseGroupField(groupBy);
+            if (this._isDateField(field)) {
+                const value = this._getGroupStartingDay(groupBy, group);
+                if (!value) {
+                    return false;
+                }
+                const fOut = FORMATS[aggregateOperator]["out"];
+                // eslint-disable-next-line no-undef
+                const date = moment(value);
+                return date.isValid() ? date.format(fOut) : false;
+            }
+            return this._sanitizeValue(group[groupBy]);
         });
     }
 
     /**
-     * @override
+     * When grouping by a time field, return
+     * the group starting day (local to the timezone)
+     * @param {string} groupBy
+     * @param {object} readGroup
+     * @returns {string | undefined}
      */
-    _sanitizeValue(value, groupBy) {
-        const { aggregateOperator, field } = this.parseGroupField(groupBy);
-        if (this._isDateField(field)) {
-            const fIn = FORMATS[aggregateOperator]["in"];
-            const fOut = FORMATS[aggregateOperator]["out"];
-            // eslint-disable-next-line no-undef
-            const date = moment(value, fIn);
-            return date.isValid() ? date.format(fOut) : false;
+    _getGroupStartingDay(groupBy, readGroup) {
+        if (!readGroup["__range"] || !readGroup["__range"][groupBy]) {
+            return undefined;
         }
-        return super._sanitizeValue(value);
+        const { field } = this.parseGroupField(groupBy);
+        const sqlValue = readGroup["__range"][groupBy].from;
+        if (this.metaData.fields[field.name].type === "date") {
+            return sqlValue;
+        }
+        return luxon.DateTime.fromSQL(sqlValue, { zone: "utc" }).toLocal().toISODate();
     }
 
     /**
diff --git a/addons/spreadsheet/static/tests/pivots/model/pivot_positional_formula_test.js b/addons/spreadsheet/static/tests/pivots/model/pivot_positional_formula_test.js
index be1f14392be..f6db0d96637 100644
--- a/addons/spreadsheet/static/tests/pivots/model/pivot_positional_formula_test.js
+++ b/addons/spreadsheet/static/tests/pivots/model/pivot_positional_formula_test.js
@@ -338,6 +338,6 @@ QUnit.module("spreadsheet > positional pivot formula", {}, () => {
                 </pivot>`,
         });
         setCellContent(model, "A1", `=ODOO.PIVOT.HEADER(1,"#date:day",1)`);
-        assert.strictEqual(getEvaluatedCell(model, "A1").formattedValue, "01/20/2016");
+        assert.strictEqual(getEvaluatedCell(model, "A1").formattedValue, "04/14/2016");
     });
 });