diff --git a/opentech/apply/projects/models.py b/opentech/apply/projects/models.py
index 4d0b0034b3ed7a9f14742ec86560abed390588b9..0053f4c3009bf2884d99efdba6de38925bec4a07 100644
--- a/opentech/apply/projects/models.py
+++ b/opentech/apply/projects/models.py
@@ -767,12 +767,6 @@ class Report(models.Model):
 
         return self.project.start_date
 
-    def serialize(self):
-        return {
-            'endDate': self.end_date,
-            'projectEndDate': self.project.end_date,
-        }
-
 
 class ReportVersion(models.Model):
     report = models.ForeignKey("Report", on_delete=models.CASCADE, related_name="versions")
diff --git a/opentech/apply/projects/templates/application_projects/includes/reports.html b/opentech/apply/projects/templates/application_projects/includes/reports.html
index 809a1bb7a1a8e51375c1473ff03390eeed1c3d28..d2e467468be3734c652acec818ca9e05e180d139 100644
--- a/opentech/apply/projects/templates/application_projects/includes/reports.html
+++ b/opentech/apply/projects/templates/application_projects/includes/reports.html
@@ -13,7 +13,7 @@
                     </p>
                     <!-- Change report frequency modal -->
                     <div class="modal" id="change-frequency">
-                        {{ object.report_config.last_report.serialize|json_script:"lastReportData" }}
+                        {{ report_data|json_script:"reportData" }}
                         <h4 class="modal__header-bar">Change reporting frequency</h4>
                         <div class="form__info-box">
                             <p>
diff --git a/opentech/apply/projects/views/project.py b/opentech/apply/projects/views/project.py
index 76e4e727ddb7542fc05d43dbb551d1d38aa148e8..aa81828677434395b5c2ae337647a7e8970b1980 100644
--- a/opentech/apply/projects/views/project.py
+++ b/opentech/apply/projects/views/project.py
@@ -438,6 +438,12 @@ class AdminProjectDetailView(
         context = super().get_context_data(**kwargs)
         context['approvals'] = self.object.approvals.distinct('by')
         context['remaining_document_categories'] = list(self.object.get_missing_document_categories())
+
+        if self.object.is_in_progress:
+            context['report_data'] = {
+                'startDate': self.object.report_config.current_due_report().start_date,
+                'projectEndDate': self.object.end_date,
+            }
         return context
 
 
diff --git a/opentech/static_src/src/javascript/apply/report-calculator.js b/opentech/static_src/src/javascript/apply/report-calculator.js
index e557bdc357d73825d8fc31addf758c66a63d8c09..c3a038c3e5a2d7d247053086f4d78ed7150690ee 100644
--- a/opentech/static_src/src/javascript/apply/report-calculator.js
+++ b/opentech/static_src/src/javascript/apply/report-calculator.js
@@ -2,7 +2,7 @@
 
     'use strict';
 
-    const reportData = JSON.parse(document.getElementById('lastReportData').textContent);
+    const reportData = JSON.parse(document.getElementById('reportData').textContent);
 
     // Form inputs
     const frequencyNumberInput = document.getElementById('id_occurrence');
@@ -39,11 +39,10 @@
         pluraliseTimePeriod(frequencyNumberInput.value);
     }
 
-    // Set the reporting period start date (endDate + 1)
+    // Set the reporting period start date 
     function setReportPeriodStart() {
-        const endDate = new Date(reportData.endDate);
-        endDate.setDate(endDate.getDate() + 1);
-        periodStartSlot.innerHTML = endDate.toISOString().slice(0, 10);
+        const startDate = new Date(reportData.startDate);
+        periodStartSlot.innerHTML = startDate.toISOString().slice(0, 10);
     }
 
     function addReportPeriodEvents() {