diff --git a/backend/app/services/report_service.py b/backend/app/services/report_service.py
index 9ea1923..88a63fc 100644
--- a/backend/app/services/report_service.py
+++ b/backend/app/services/report_service.py
@@ -94,7 +94,7 @@ def _empty_ta_weekly_row(kw: int) -> dict:
 # Sheet 1: Auswertung KW gesamt
 # ---------------------------------------------------------------------------
 
-def calculate_sheet1_data(db: Session, jahr: int) -> dict:
+def calculate_sheet1_data(db: Session, jahr: int, max_kw: int | None = None) -> dict:
     """Calculate *Auswertung KW gesamt*.
 
     Returns::
@@ -121,8 +121,13 @@ def calculate_sheet1_data(db: Session, jahr: int) -> dict:
     * Ablehnungen    = cases where ablehnung == True
     * Gutachten      = cases where gutachten == True
     * Keine RM       = Unterlagen - Gutachten  (derived, per KW row)
+
+    If *max_kw* is given, only data up to and including that KW is included.
     """
     # One query: group by kw, count the four flags
+    filters = [Case.versicherung == settings.VERSICHERUNG_FILTER, Case.jahr == jahr]
+    if max_kw is not None:
+        filters.append(Case.kw <= max_kw)
     rows = (
         db.query(
             Case.kw,
@@ -131,7 +136,7 @@ def calculate_sheet1_data(db: Session, jahr: int) -> dict:
             func.sum(Case.ablehnung.cast(Integer)).label("ablehnungen"),
             func.sum(Case.gutachten.cast(Integer)).label("gutachten"),
         )
-        .filter(Case.versicherung == settings.VERSICHERUNG_FILTER, Case.jahr == jahr)
+        .filter(*filters)
         .group_by(Case.kw)
         .all()
     )
@@ -178,7 +183,7 @@ def calculate_sheet1_data(db: Session, jahr: int) -> dict:
 # Sheet 2: Auswertung nach Fachgebieten
 # ---------------------------------------------------------------------------
 
-def calculate_sheet2_data(db: Session, jahr: int) -> dict:
+def calculate_sheet2_data(db: Session, jahr: int, max_kw: int | None = None) -> dict:
     """Calculate *Auswertung nach Fachgebieten*.
 
     Per KW, per Fallgruppe: Anzahl, Gutachten, Keine RM/Ablehnung.
@@ -200,7 +205,12 @@ def calculate_sheet2_data(db: Session, jahr: int) -> dict:
         }
 
     Keine RM/Ablehnung = Anzahl - Gutachten  (per the Excel formula).
+
+    If *max_kw* is given, only data up to and including that KW is included.
     """
+    filters = [Case.versicherung == settings.VERSICHERUNG_FILTER, Case.jahr == jahr]
+    if max_kw is not None:
+        filters.append(Case.kw <= max_kw)
     rows = (
         db.query(
             Case.kw,
@@ -208,7 +218,7 @@ def calculate_sheet2_data(db: Session, jahr: int) -> dict:
             func.count(Case.id).label("anzahl"),
             func.sum(Case.gutachten.cast(Integer)).label("gutachten"),
         )
-        .filter(Case.versicherung == settings.VERSICHERUNG_FILTER, Case.jahr == jahr)
+        .filter(*filters)
         .group_by(Case.kw, Case.fallgruppe)
         .all()
     )
@@ -242,7 +252,7 @@ def calculate_sheet2_data(db: Session, jahr: int) -> dict:
 # Sheet 3: Auswertung Gutachten
 # ---------------------------------------------------------------------------
 
-def calculate_sheet3_data(db: Session, jahr: int) -> dict:
+def calculate_sheet3_data(db: Session, jahr: int, max_kw: int | None = None) -> dict:
     """Calculate *Auswertung Gutachten*.
 
     Per KW, per group (gesamt + 5 Fallgruppen):
@@ -269,7 +279,16 @@ def calculate_sheet3_data(db: Session, jahr: int) -> dict:
     - Per Fallgruppe: Gutachten = count, Alternative = count where typ='Alternative',
       Bestaetigung = Gutachten - Alternative
     - Gesamt = sum across all Fallgruppen
+
+    If *max_kw* is given, only data up to and including that KW is included.
     """
+    filters = [
+        Case.versicherung == settings.VERSICHERUNG_FILTER,
+        Case.jahr == jahr,
+        Case.gutachten == True,  # noqa: E712
+    ]
+    if max_kw is not None:
+        filters.append(Case.kw <= max_kw)
     rows = (
         db.query(
             Case.kw,
@@ -279,7 +298,7 @@ def calculate_sheet3_data(db: Session, jahr: int) -> dict:
                 (Case.gutachten_typ == "Alternative").cast(Integer)
             ).label("alternative"),
         )
-        .filter(Case.versicherung == settings.VERSICHERUNG_FILTER, Case.jahr == jahr, Case.gutachten == True)  # noqa: E712
+        .filter(*filters)
         .group_by(Case.kw, Case.fallgruppe)
         .all()
     )
@@ -322,7 +341,7 @@ def calculate_sheet3_data(db: Session, jahr: int) -> dict:
 # Sheet 4: Auswertung Therapieaenderungen
 # ---------------------------------------------------------------------------
 
-def calculate_sheet4_data(db: Session, jahr: int) -> dict:
+def calculate_sheet4_data(db: Session, jahr: int, max_kw: int | None = None) -> dict:
     """Calculate *Auswertung Therapieaenderungen*.
 
     Per KW: Gutachten count, TA Ja, TA Nein, Diagnosekorrektur,
@@ -344,7 +363,16 @@ def calculate_sheet4_data(db: Session, jahr: int) -> dict:
                 ...
             ]
         }
+
+    If *max_kw* is given, only data up to and including that KW is included.
     """
+    filters = [
+        Case.versicherung == settings.VERSICHERUNG_FILTER,
+        Case.jahr == jahr,
+        Case.gutachten == True,  # noqa: E712
+    ]
+    if max_kw is not None:
+        filters.append(Case.kw <= max_kw)
     rows = (
         db.query(
             Case.kw,
@@ -359,7 +387,7 @@ def calculate_sheet4_data(db: Session, jahr: int) -> dict:
             func.sum(Case.ta_unterversorgung.cast(Integer)).label("unterversorgung"),
             func.sum(Case.ta_uebertherapie.cast(Integer)).label("uebertherapie"),
         )
-        .filter(Case.versicherung == settings.VERSICHERUNG_FILTER, Case.jahr == jahr, Case.gutachten == True)  # noqa: E712
+        .filter(*filters)
         .group_by(Case.kw)
         .all()
     )
@@ -388,7 +416,7 @@ def calculate_sheet4_data(db: Session, jahr: int) -> dict:
 # Sheet 5: Auswertung ICD onko
 # ---------------------------------------------------------------------------
 
-def calculate_sheet5_data(db: Session, jahr: int) -> dict:
+def calculate_sheet5_data(db: Session, jahr: int, max_kw: int | None = None) -> dict:
     """Calculate *Auswertung ICD onko*.
 
     Returns sorted list of ICD codes from onko cases with counts.
@@ -407,20 +435,23 @@ def calculate_sheet5_data(db: Session, jahr: int) -> dict:
                 ...
             ]
         }
+
+    If *max_kw* is given, only data up to and including that KW is included.
     """
+    filter_conditions = [
+        Case.versicherung == settings.VERSICHERUNG_FILTER,
+        Case.fallgruppe == "onko",
+        Case.jahr == jahr,
+    ]
+    if max_kw is not None:
+        filter_conditions.append(Case.kw <= max_kw)
     rows = (
         db.query(
             func.upper(CaseICDCode.icd_code).label("icd"),
             func.count(CaseICDCode.id).label("cnt"),
         )
         .join(Case, CaseICDCode.case_id == Case.id)
-        .filter(
-            and_(
-                Case.versicherung == settings.VERSICHERUNG_FILTER,
-                Case.fallgruppe == "onko",
-                Case.jahr == jahr,
-            )
-        )
+        .filter(and_(*filter_conditions))
         .group_by(func.upper(CaseICDCode.icd_code))
         .order_by(func.count(CaseICDCode.id).desc(), func.upper(CaseICDCode.icd_code))
         .all()
@@ -550,8 +581,9 @@ def calculate_dashboard_kpis(db: Session, jahr: int) -> dict:
 def generate_full_report(db: Session, jahr: int, kw: int | None = None) -> dict:
     """Generate complete report data for all 5 sheets.
 
-    The *kw* parameter is recorded for metadata but does not filter the data
-    -- all sheets always contain the full year up to the latest available KW.
+    If *kw* is given, only data up to and including that calendar week is
+    included in the report.  This allows generating historical reports
+    that reflect the state at a specific point in the year.
 
     Returns::
 
@@ -570,9 +602,9 @@ def generate_full_report(db: Session, jahr: int, kw: int | None = None) -> dict:
     return {
         "jahr": jahr,
         "kw": kw,
-        "sheet1": calculate_sheet1_data(db, jahr),
-        "sheet2": calculate_sheet2_data(db, jahr),
-        "sheet3": calculate_sheet3_data(db, jahr),
-        "sheet4": calculate_sheet4_data(db, jahr),
-        "sheet5": calculate_sheet5_data(db, jahr),
+        "sheet1": calculate_sheet1_data(db, jahr, max_kw=kw),
+        "sheet2": calculate_sheet2_data(db, jahr, max_kw=kw),
+        "sheet3": calculate_sheet3_data(db, jahr, max_kw=kw),
+        "sheet4": calculate_sheet4_data(db, jahr, max_kw=kw),
+        "sheet5": calculate_sheet5_data(db, jahr, max_kw=kw),
     }