diff --git a/js/calendar.js b/js/calendar.js
new file mode 100644
index 0000000..f1340b1
--- /dev/null
+++ b/js/calendar.js
@@ -0,0 +1,245 @@
+import { state } from './app.js';
+import { getWorkdays, generatePlan } from './algorithm.js';
+import { toggleHoliday, toggleClosure, addHistoryEntries } from './data.js';
+import { exportSchedule, downloadBlob } from './excel.js';
+
+const MONTHS = ['Januar','Februar','März','April','Mai','Juni',
+  'Juli','August','September','Oktober','November','Dezember'];
+const WD_LABELS = ['Mo','Di','Mi','Do','Fr','Sa','So'];
+
+let currentYear = 2026;
+let currentMonth = Math.min(Math.max(new Date().getMonth() + 1, 1), 12);
+let currentPlan = []; // [{ date, employeeId, manual }] for displayed month
+
+export function renderCalendar() {
+  const container = document.getElementById('tab-planning');
+  container.replaceChildren();
+
+  // Title
+  const title = document.createElement('h2');
+  title.className = 'section-title';
+  title.textContent = 'Monatsplanung';
+  container.appendChild(title);
+
+  // Controls row
+  const controls = document.createElement('div');
+  controls.className = 'row';
+
+  const monthLabel = document.createElement('label');
+  monthLabel.textContent = 'Monat:';
+
+  const monthSel = document.createElement('select');
+  MONTHS.forEach((m, i) => {
+    const opt = document.createElement('option');
+    opt.value = String(i + 1);
+    opt.textContent = m;
+    if (i + 1 === currentMonth) opt.selected = true;
+    monthSel.appendChild(opt);
+  });
+
+  const yearLabel = document.createElement('label');
+  yearLabel.textContent = 'Jahr:';
+
+  const yearSel = document.createElement('select');
+  const yearOpt = document.createElement('option');
+  yearOpt.value = '2026';
+  yearOpt.textContent = '2026';
+  yearOpt.selected = true;
+  yearSel.appendChild(yearOpt);
+
+  const genBtn = document.createElement('button');
+  genBtn.type = 'button';
+  genBtn.className = 'primary';
+  genBtn.textContent = 'Plan generieren';
+
+  const exportBtn = document.createElement('button');
+  exportBtn.type = 'button';
+  exportBtn.textContent = 'Als Excel exportieren';
+  exportBtn.style.display = 'none';
+
+  controls.append(monthLabel, monthSel, yearLabel, yearSel, genBtn, exportBtn);
+  container.appendChild(controls);
+
+  // Legend
+  const legend = document.createElement('div');
+  legend.className = 'row';
+  legend.style.cssText = 'font-size:12px;color:#6b7280';
+  legend.textContent = 'FT = Feiertag markieren  |  BU = Betriebsurlaub markieren';
+  container.appendChild(legend);
+
+  // Calendar grid wrapper
+  const wrapper = document.createElement('div');
+  wrapper.className = 'calendar-outer';
+  wrapper.id = 'calendar-wrapper';
+  container.appendChild(wrapper);
+
+  loadPlanFromHistory();
+  renderGrid(wrapper, exportBtn);
+
+  monthSel.addEventListener('change', () => {
+    currentMonth = parseInt(monthSel.value);
+    loadPlanFromHistory();
+    renderGrid(wrapper, exportBtn);
+  });
+
+  genBtn.addEventListener('click', () => {
+    if (state.employees.length === 0) {
+      alert('Bitte zuerst Mitarbeiter hinzufügen.');
+      return;
+    }
+    const workdays = getWorkdays(currentYear, currentMonth,
+      state.calendar.holidays, state.calendar.companyClosures);
+    const prefix = currentYear + '-' + String(currentMonth).padStart(2,'0');
+    const historyWithoutMonth = state.history.filter(h => !h.date.startsWith(prefix));
+    currentPlan = generatePlan(workdays, state.employees, historyWithoutMonth);
+    addHistoryEntries(state, currentPlan);
+    renderGrid(wrapper, exportBtn);
+  });
+
+  exportBtn.addEventListener('click', () => {
+    const blob = exportSchedule(currentPlan, state.employees);
+    downloadBlob(blob, 'Moderationsplan-' + MONTHS[currentMonth-1] + '-' + currentYear + '.xlsx');
+  });
+}
+
+function loadPlanFromHistory() {
+  const prefix = currentYear + '-' + String(currentMonth).padStart(2,'0');
+  currentPlan = state.history
+    .filter(h => h.date.startsWith(prefix))
+    .map(h => ({ ...h }));
+}
+
+function renderGrid(wrapper, exportBtn) {
+  wrapper.replaceChildren();
+
+  const daysInMonth = new Date(currentYear, currentMonth, 0).getDate();
+  const nameById = Object.fromEntries(state.employees.map(e => [e.id, e.name]));
+  const planByDate = Object.fromEntries(currentPlan.map(a => [a.date, a.employeeId]));
+
+  // Day-of-week header row
+  const headerGrid = document.createElement('div');
+  headerGrid.className = 'calendar-header-grid';
+  WD_LABELS.forEach(lbl => {
+    const cell = document.createElement('div');
+    cell.style.cssText = 'text-align:center;font-weight:600;font-size:12px;color:#6b7280;padding:4px';
+    cell.textContent = lbl;
+    headerGrid.appendChild(cell);
+  });
+  wrapper.appendChild(headerGrid);
+
+  // Body grid
+  const bodyGrid = document.createElement('div');
+  bodyGrid.className = 'calendar-body-grid';
+
+  // Offset empty cells before first day
+  const firstISO = currentYear + '-' + String(currentMonth).padStart(2,'0') + '-01';
+  const firstWD = (() => { const d = new Date(firstISO + 'T12:00:00Z').getUTCDay(); return d === 0 ? 7 : d; })();
+  for (let i = 1; i < firstWD; i++) {
+    const empty = document.createElement('div');
+    empty.className = 'cal-day empty-cell';
+    bodyGrid.appendChild(empty);
+  }
+
+  // Day cells
+  for (let d = 1; d <= daysInMonth; d++) {
+    const iso = currentYear + '-' + String(currentMonth).padStart(2,'0') + '-' + String(d).padStart(2,'0');
+    const wdNum = (() => { const x = new Date(iso + 'T12:00:00Z').getUTCDay(); return x === 0 ? 7 : x; })();
+    const isWeekend = wdNum >= 6;
+    const isHoliday = state.calendar.holidays.includes(iso);
+    const isClosure = state.calendar.companyClosures.includes(iso);
+    const assigneeId = planByDate[iso];
+
+    const cell = document.createElement('div');
+    cell.className = 'cal-day';
+    if (isWeekend) cell.classList.add('weekend');
+    else if (isHoliday) cell.classList.add('holiday');
+    else if (isClosure) cell.classList.add('closure');
+
+    // Day number + weekday label
+    const dayNum = document.createElement('div');
+    dayNum.className = 'day-num';
+    dayNum.textContent = d + ' ';
+    const wdSpan = document.createElement('span');
+    wdSpan.className = 'day-tag';
+    wdSpan.textContent = WD_LABELS[wdNum - 1];
+    dayNum.appendChild(wdSpan);
+    cell.appendChild(dayNum);
+
+    if (!isWeekend) {
+      if (isHoliday || isClosure) {
+        // Show label + remove button
+        const tag = document.createElement('div');
+        tag.style.cssText = 'font-size:11px;margin-top:4px';
+        tag.textContent = isHoliday ? 'Feiertag' : 'Betriebsurlaub';
+        const removeBtn = document.createElement('button');
+        removeBtn.type = 'button';
+        removeBtn.textContent = '✕';
+        removeBtn.style.cssText = 'font-size:9px;padding:1px 4px;margin-left:4px';
+        removeBtn.addEventListener('click', () => {
+          if (isHoliday) toggleHoliday(state, iso);
+          else toggleClosure(state, iso);
+          renderGrid(wrapper, exportBtn);
+        });
+        tag.appendChild(removeBtn);
+        cell.appendChild(tag);
+      } else {
+        // Assignee dropdown
+        const sel = document.createElement('select');
+        sel.style.cssText = 'width:100%;margin-top:4px;font-size:11px';
+
+        const emptyOpt = document.createElement('option');
+        emptyOpt.value = '';
+        emptyOpt.textContent = '— Leer —';
+        sel.appendChild(emptyOpt);
+
+        for (const emp of state.employees) {
+          const opt = document.createElement('option');
+          opt.value = emp.id;
+          opt.textContent = emp.name; // textContent: safe
+          if (emp.id === assigneeId) opt.selected = true;
+          sel.appendChild(opt);
+        }
+
+        sel.addEventListener('change', () => {
+          const empId = sel.value;
+          if (empId) {
+            const entry = { date: iso, employeeId: empId, manual: true };
+            addHistoryEntries(state, [entry]);
+            const idx = currentPlan.findIndex(a => a.date === iso);
+            if (idx >= 0) currentPlan[idx] = entry; else currentPlan.push(entry);
+          } else {
+            state.history = state.history.filter(h => h.date !== iso);
+            currentPlan = currentPlan.filter(a => a.date !== iso);
+          }
+          exportBtn.style.display = currentPlan.length > 0 ? 'inline-block' : 'none';
+        });
+
+        cell.appendChild(sel);
+
+        // FT / BU mark buttons
+        const btnRow = document.createElement('div');
+        btnRow.style.cssText = 'margin-top:4px;display:flex;gap:2px';
+
+        const ftBtn = document.createElement('button');
+        ftBtn.type = 'button';
+        ftBtn.textContent = 'FT';
+        ftBtn.style.cssText = 'font-size:9px;padding:1px 4px';
+        ftBtn.addEventListener('click', () => { toggleHoliday(state, iso); renderGrid(wrapper, exportBtn); });
+
+        const buBtn = document.createElement('button');
+        buBtn.type = 'button';
+        buBtn.textContent = 'BU';
+        buBtn.style.cssText = 'font-size:9px;padding:1px 4px';
+        buBtn.addEventListener('click', () => { toggleClosure(state, iso); renderGrid(wrapper, exportBtn); });
+
+        btnRow.append(ftBtn, buBtn);
+        cell.appendChild(btnRow);
+      }
+    }
+
+    bodyGrid.appendChild(cell);
+  }
+
+  wrapper.appendChild(bodyGrid);
+  exportBtn.style.display = currentPlan.length > 0 ? 'inline-block' : 'none';
+}