diff --git a/public/monatsvorhersage.php b/public/monatsvorhersage.php
index 3d4422b..f26f87d 100644
--- a/public/monatsvorhersage.php
+++ b/public/monatsvorhersage.php
@@ -11,6 +11,8 @@ $publicBasePath = './';
 $currentYear = (int) date('Y');
 $selectedYear = isset($_GET['year']) ? (int) $_GET['year'] : $currentYear;
 $selectedMonth = isset($_GET['month']) ? max(1, min(12, (int) $_GET['month'])) : (int) date('n');
+$selectedWeek = isset($_GET['week']) ? max(1, min(53, (int) $_GET['week'])) : (int) date('W');
+$selectedWeekYear = isset($_GET['week_year']) ? (int) $_GET['week_year'] : $currentYear;
 $shouldRunForecast = isset($_GET['run']) && $_GET['run'] === '1';
 
 // -------------------------------------------------------------------------
@@ -178,7 +180,16 @@ $favoriteCometVisibilityMaxMagnitude = 10.0;
 // Einzelne Zufallstreffer sollen nicht als eigenes Monatsereignis erscheinen.
 $favoriteCometVisibilityMinConsecutiveDays = 2;
 
+if (!function_exists('getIsoWeekCountForYear')) {
+    function getIsoWeekCountForYear(int $year): int
+    {
+        return (int) (new DateTimeImmutable(sprintf('%04d-12-28', $year)))->format('W');
+    }
+}
+
 $years = range($currentYear - 2, $currentYear + 5);
+$selectedWeek = max(1, min($selectedWeek, getIsoWeekCountForYear($selectedWeekYear)));
+$weekNumbers = range(1, getIsoWeekCountForYear($selectedWeekYear));
 $months = [
     1 => 'Januar',
     2 => 'Februar',
@@ -2399,7 +2410,13 @@ $observationTipCalendarFilenameJson = json_encode(sprintf('astrotools-monatserei
         <p>Die Sternkarte wird für den 15. des gewählten Monats mit der festen Monatsuhrzeit erzeugt.</p>
       </div>
 
-      <input type="hidden" name="run" value="1">
+      <section class="monatsvorhersage-mode">
+        <div class="monatsvorhersage-mode-header">
+          <h4>Monat</h4>
+          <p>Bestehende Monatsansicht mit Berechnung per Button.</p>
+        </div>
+
+        <input type="hidden" name="run" value="1">
 
       <label class="monatsvorhersage-field">
         <span>Jahr</span>
@@ -2423,9 +2440,44 @@ $observationTipCalendarFilenameJson = json_encode(sprintf('astrotools-monatserei
         </select>
       </label>
 
-      <div class="monatsvorhersage-actions">
-        <button type="submit">Monatsvorhersage berechnen</button>
-      </div>
+        <div class="monatsvorhersage-actions">
+          <button type="submit">Monatsvorhersage berechnen</button>
+        </div>
+      </section>
+
+      <section class="monatsvorhersage-mode monatsvorhersage-mode-disabled" aria-labelledby="wochenauswahl-heading">
+        <div class="monatsvorhersage-mode-header">
+          <h4 id="wochenauswahl-heading">Woche</h4>
+          <p>Nur vorbereitete GUI. Die Wochenberechnung ist noch nicht angeschlossen.</p>
+        </div>
+
+        <label class="monatsvorhersage-field">
+          <span>Jahr</span>
+          <select name="week_year" id="weekYearSelect">
+            <?php foreach ($years as $year): ?>
+              <option value="<?= htmlspecialchars((string) $year, ENT_QUOTES, 'UTF-8') ?>" <?= $year === $selectedWeekYear ? 'selected' : '' ?>>
+                <?= htmlspecialchars((string) $year, ENT_QUOTES, 'UTF-8') ?>
+              </option>
+            <?php endforeach; ?>
+          </select>
+        </label>
+
+        <label class="monatsvorhersage-field">
+          <span>Woche</span>
+          <select name="week" id="weekSelect">
+            <?php foreach ($weekNumbers as $weekNumber): ?>
+              <?php $weekStartLabel = (new DateTimeImmutable('now'))->setISODate($selectedWeekYear, $weekNumber, 1)->format('d.m.Y'); ?>
+              <option value="<?= htmlspecialchars((string) $weekNumber, ENT_QUOTES, 'UTF-8') ?>" <?= $weekNumber === $selectedWeek ? 'selected' : '' ?>>
+                <?= htmlspecialchars('KW ' . str_pad((string) $weekNumber, 2, '0', STR_PAD_LEFT) . ' (' . $weekStartLabel . ')', ENT_QUOTES, 'UTF-8') ?>
+              </option>
+            <?php endforeach; ?>
+          </select>
+        </label>
+
+        <div class="monatsvorhersage-actions">
+          <button type="button" disabled>Wochenansicht folgt spaeter</button>
+        </div>
+      </section>
     </form>
 
     <?php if ($shouldRunForecast): ?>
@@ -2590,6 +2642,37 @@ $observationTipCalendarFilenameJson = json_encode(sprintf('astrotools-monatserei
   padding: 22px 20px;
 }
 
+.monatsvorhersage-mode {
+  display: grid;
+  grid-template-columns: repeat(2, minmax(0, 1fr));
+  gap: 16px;
+  align-content: start;
+  padding: 18px;
+  border: 1px solid rgba(108, 145, 220, 0.2);
+  border-radius: 16px;
+  background: rgba(6, 12, 24, 0.38);
+}
+
+.monatsvorhersage-mode-disabled {
+  border-color: rgba(201, 168, 76, 0.18);
+  background: rgba(18, 18, 22, 0.34);
+}
+
+.monatsvorhersage-mode-header {
+  grid-column: 1 / -1;
+}
+
+.monatsvorhersage-mode-header h4 {
+  margin: 0 0 6px;
+  font-size: 1.05rem;
+}
+
+.monatsvorhersage-mode-header p {
+  margin: 0;
+  color: rgba(222, 232, 255, 0.78);
+  line-height: 1.6;
+}
+
 .monatsvorhersage-form-header,
 .monatskarte-header,
 .monatskarte-footer {
@@ -2650,6 +2733,13 @@ $observationTipCalendarFilenameJson = json_encode(sprintf('astrotools-monatserei
   cursor: pointer;
 }
 
+.monatsvorhersage-mode-disabled .monatsvorhersage-actions button {
+  border-color: rgba(180, 186, 205, 0.38);
+  background: rgba(48, 54, 70, 0.7);
+  color: rgba(226, 232, 244, 0.76);
+  cursor: not-allowed;
+}
+
 .monatskarte-header {
   display: flex;
   justify-content: space-between;
@@ -2761,6 +2851,10 @@ $observationTipCalendarFilenameJson = json_encode(sprintf('astrotools-monatserei
     grid-template-columns: 1fr;
   }
 
+  .monatsvorhersage-mode {
+    grid-template-columns: 1fr;
+  }
+
   .monatskarte-header {
     flex-direction: column;
   }
@@ -2785,6 +2879,69 @@ const OBSERVATION_TIP_ICAL_FILENAME = <?= $observationTipCalendarFilenameJson ?:
 const MONTH_CHART_COMET_K = 0.01720209895;
 const MONTH_CHART_COMET_OBLIQ = 23.439279444444445 * Math.PI / 180;
 
+function isoWeekCount(year) {
+  const dec28 = new Date(Date.UTC(year, 11, 28));
+  const day = dec28.getUTCDay() || 7;
+  dec28.setUTCDate(dec28.getUTCDate() + 4 - day);
+  const yearStart = new Date(Date.UTC(dec28.getUTCFullYear(), 0, 1));
+  return Math.ceil((((dec28 - yearStart) / 86400000) + 1) / 7);
+}
+
+function isoWeekMonday(year, week) {
+  const jan4 = new Date(Date.UTC(year, 0, 4));
+  const jan4Day = jan4.getUTCDay() || 7;
+  const monday = new Date(jan4);
+  monday.setUTCDate(jan4.getUTCDate() - jan4Day + 1 + ((week - 1) * 7));
+  return monday;
+}
+
+function formatGermanDate(date) {
+  const day = String(date.getUTCDate()).padStart(2, '0');
+  const month = String(date.getUTCMonth() + 1).padStart(2, '0');
+  const year = String(date.getUTCFullYear());
+  return day + '.' + month + '.' + year;
+}
+
+function rebuildWeekOptions() {
+  const weekYearSelect = document.getElementById('weekYearSelect');
+  const weekSelect = document.getElementById('weekSelect');
+
+  if (!weekYearSelect || !weekSelect) {
+    return;
+  }
+
+  const selectedYear = Number(weekYearSelect.value);
+  if (!Number.isInteger(selectedYear) || selectedYear < 1) {
+    return;
+  }
+
+  const previousWeek = Number(weekSelect.value) || 1;
+  const totalWeeks = isoWeekCount(selectedYear);
+  const nextWeek = Math.min(Math.max(previousWeek, 1), totalWeeks);
+
+  weekSelect.innerHTML = '';
+
+  for (let week = 1; week <= totalWeeks; week++) {
+    const option = document.createElement('option');
+    option.value = String(week);
+    option.textContent = 'KW ' + String(week).padStart(2, '0') + ' (' + formatGermanDate(isoWeekMonday(selectedYear, week)) + ')';
+    if (week === nextWeek) {
+      option.selected = true;
+    }
+    weekSelect.appendChild(option);
+  }
+}
+
+document.addEventListener('DOMContentLoaded', function () {
+  const weekYearSelect = document.getElementById('weekYearSelect');
+  if (!weekYearSelect) {
+    return;
+  }
+
+  rebuildWeekOptions();
+  weekYearSelect.addEventListener('change', rebuildWeekOptions);
+});
+
 function monthChartCometSolveElliptic(M, e) {
   let E = e < 0.8 ? M : (M >= 0 ? Math.PI : -Math.PI);
   for (let i = 0; i < 30; i++) {