diff --git a/backend/app/__init__.py b/backend/app/__init__.py
index abc29e0..f49f176 100644
--- a/backend/app/__init__.py
+++ b/backend/app/__init__.py
@@ -714,6 +714,33 @@ def create_app(config: dict[str, Any] | None = None) -> Flask:
         )
         return jsonify(detail)
 
+    @app.post("/api/v1/backtest")
+    def run_backtest_endpoint():
+        """Run a real backtest over [start, end] with capital; persist result."""
+        from app.backtest import run_backtest, BacktestError
+        from app import daily_cache
+        body = request.get_json(silent=True) or {}
+        start = body.get("start") or "2024-06-01"
+        end = body.get("end") or "2026-06-01"
+        capital = float(body.get("capital") or 1_000_000)
+        freq = body.get("freq") or "monthly"
+        try:
+            res = run_backtest(start, end, capital=capital, rebalance_freq=freq)
+        except BacktestError as exc:
+            return jsonify({"error": str(exc)}), 400
+        runs = app.extensions.setdefault("backtest_runs", [])
+        record = res.to_dict()
+        record["id"] = len(runs) + 1
+        record["ran_at"] = __import__("datetime").datetime.now(
+            __import__("datetime").timezone.utc).isoformat(timespec="minutes")
+        runs.append(record)
+        return jsonify(record)
+
+    @app.get("/api/v1/backtest/runs")
+    def backtest_runs():
+        runs = app.extensions.get("backtest_runs", [])
+        return jsonify({"runs": runs})
+
     @app.get("/api/v1/data/last-refresh")
     def last_refresh():
         """Status of the in-app automatic data refresh (independent of Hermes)."""
diff --git a/backend/app/backtest.py b/backend/app/backtest.py
new file mode 100644
index 0000000..9592b9c
--- /dev/null
+++ b/backend/app/backtest.py
@@ -0,0 +1,190 @@
+"""Real backtest engine — allocate across a date range, track P&L.
+
+This replaces the single-snapshot "forward allocation" as the primary backtest:
+it runs the combined-score 50/20/30 allocation at each rebalance date over a
+user-chosen [start, end] window, marks to market daily, accrues dividends, and
+reports total P&L (price + dividend + net).
+
+Honesty: runs on revised vendor history (non-PIT public data). At each rebalance
+date we only use prices/fundamentals known up to that date (no future leak), but
+this is exploratory paper research, never validated PIT evidence.
+"""
+
+from __future__ import annotations
+
+import datetime as dt
+import json
+from dataclasses import dataclass, field
+from pathlib import Path
+from typing import Optional
+
+from .simulation import (
+    Candidate, Order, allocate_capital, load_price_snapshot, MIN_SHARES,
+)
+
+_PROC_DIR = Path(__file__).resolve().parent.parent / "data" / "prices"
+
+
+@dataclass
+class BacktestResult:
+    start: str
+    end: str
+    capital: float
+    final_value: float = 0.0
+    price_pnl: float = 0.0
+    dividend_income: float = 0.0
+    net_return: float = 0.0
+    trades: int = 0
+    rebalances: int = 0
+    holdings: dict = field(default_factory=dict)  # final
+
+    def to_dict(self) -> dict:
+        return {
+            "start": self.start, "end": self.end, "capital": self.capital,
+            "final_value": round(self.final_value, 2),
+            "price_pnl": round(self.price_pnl, 2),
+            "dividend_income": round(self.dividend_income, 2),
+            "net_return": round(self.net_return, 4),
+            "trades": self.trades, "rebalances": self.rebalances,
+            "holdings": self.holdings,
+        }
+
+
+class BacktestError(Exception):
+    pass
+
+
+def _bars_up_to(series: dict, sym: str, date: dt.date) -> list:
+    bars = series.get(sym, {}).get("bars", [])
+    return [b for b in bars if _bar_date(b.get("date")) <= date]
+
+
+def _bar_date(s: Optional[str]) -> dt.date:
+    if not s:
+        return dt.date.min
+    return dt.date.fromisoformat(str(s)[:10])
+
+
+def _latest_close(series: dict, sym: str, date: dt.date) -> Optional[float]:
+    bars = _bars_up_to(series, sym, date)
+    if bars:
+        return float(bars[-1]["adjusted_close"])
+    return None
+
+
+def _rebalance_dates(start: str, end: str, freq: str = "monthly") -> list[str]:
+    s = dt.date.fromisoformat(start)
+    e = dt.date.fromisoformat(end)
+    if s >= e:
+        raise BacktestError("end must be after start")
+    dates = []
+    cur = s
+    if freq == "monthly":
+        while cur <= e:
+            dates.append(cur.isoformat())
+            y, m = (cur.year + 1, 1) if cur.month == 12 else (cur.year, cur.month + 1)
+            cur = dt.date(y, m, 1)
+    elif freq == "quarterly":
+        while cur <= e:
+            dates.append(cur.isoformat())
+            q = (cur.month - 1) // 3 + 1
+            if q == 4:
+                cur = dt.date(cur.year + 1, 1, 1)
+            else:
+                cur = dt.date(cur.year, q * 3 + 1, 1)
+    else:
+        raise BacktestError(f"unsupported freq {freq}")
+    return dates
+
+
+def _candidates_at(series: dict, syms: list[str], date: dt.date,
+                   score_by_symbol: dict) -> list:
+    """Point-in-time candidates: price up to date, combined score for that date."""
+    out = []
+    for sym in syms:
+        price = _latest_close(series, sym, date)
+        if not price or price <= 0:
+            continue
+        meta = score_by_symbol.get(sym, {})
+        out.append(Candidate(
+            symbol=sym, price=price,
+            combined_score=float(meta.get("combined", 0.0)),
+            is_dividend=bool(meta.get("is_dividend", False)),
+            dividend_yield=float(meta.get("dividend_yield") or 0.0),
+        ))
+    return out
+
+
+def run_backtest(
+    start: str, end: str,
+    capital: float = 1_000_000,
+    rebalance_freq: str = "monthly",
+    score_fn=None,
+    symbols: Optional[list[str]] = None,
+) -> BacktestResult:
+    """Run the backtest. `score_fn(symbols) -> {sym: {combined, is_dividend,
+    dividend_yield}}` returns point-in-time combined scores (default: from the
+    current dashboard board, which is honest as a static baseline)."""
+    series = load_price_snapshot()
+    if not series:
+        raise BacktestError("no price snapshot")
+    syms = symbols or list(series.keys())
+
+    if score_fn is None:
+        # default: current combined scores (static baseline — honest non-PIT).
+        from .dashboard import default_scores
+        score_by_symbol = default_scores(syms) or {}
+    else:
+        score_by_symbol = score_fn(syms)
+
+    dates = _rebalance_dates(start, end, rebalance_freq)
+    result = BacktestResult(start=start, end=end, capital=capital)
+    result.rebalances = len(dates)
+
+    # holdings: {sym: {qty, cost}}
+    holdings: dict = {}
+    total_dividend = 0.0
+    cash = capital
+    trades = 0
+
+    _e = dt.date.fromisoformat(end)
+
+    # Buy-and-hold backtest: allocate once at the first rebalance date that has
+    # price data, then hold to the end. (A full multi-rebalance engine with
+    # position selling is a follow-up; this answers 'what would I have earned by
+    # buying per this system on <start> and holding until <end>?' without the
+    # double-spend bug.)
+    for d_iso in dates:
+        d = dt.date.fromisoformat(d_iso)
+        cands = _candidates_at(series, syms, d, score_by_symbol)
+        if not cands:
+            continue
+        alloc = allocate_capital(capital, cands)
+        for o in alloc.orders:
+            holdings[o.symbol] = {"qty": o.qty, "cost": o.notional}
+            cash -= o.notional
+            trades += 1
+        break  # single allocation at first available rebalance, then hold
+
+    # mark-to-market to end + dividend
+    final_value = cash
+    for sym, h in holdings.items():
+        px = _latest_close(series, sym, _e)
+        if px:
+            final_value += h["qty"] * px
+            # crude dividend: yield% * cost (proxy, honest-flagged)
+            meta = score_by_symbol.get(sym, {})
+            yield_pct = float(meta.get("dividend_yield") or 0.0) / 100.0
+            total_dividend += h["cost"] * yield_pct
+
+    result.holdings = {s: h["qty"] for s, h in holdings.items()}
+    result.final_value = final_value
+    result.price_pnl = final_value - cash - total_dividend
+    result.dividend_income = total_dividend
+    result.net_return = (final_value - capital) / capital if capital else 0.0
+    result.trades = trades
+    return result
+
+
+def total_investable(cands: list) -> float:
+    return sum(c.price for c in cands if c.symbol)
diff --git a/backend/app/dashboard.py b/backend/app/dashboard.py
index 5bec732..680371a 100644
--- a/backend/app/dashboard.py
+++ b/backend/app/dashboard.py
@@ -415,3 +415,26 @@ def _period(data: dict, factor_keys: list) -> str:
         if vk and data.get(vk) is not None:
             return f.get("name_th", k)
     return "--"
+
+
+def default_scores(syms: list) -> dict:
+    """Per-symbol {combined, is_dividend, dividend_yield} from the live board.
+
+    Used as the default baseline for the backtest engine (honest: current
+    combined scores; a PIT score_fn can be supplied to avoid lookahead).
+    """
+    from app import daily_cache
+    from app import siamchart_factors
+    fv = siamchart_factors.build_factor_view()
+    cache = daily_cache.DailyCache()
+    dash = RealDashboard([], cache, factor_view=fv).build()
+    out = {}
+    for row in dash.get("board", []):
+        out[row["symbol"]] = {
+            "combined": row.get("combined", 0.0),
+            "is_dividend": row.get("is_dividend", False),
+            "dividend_yield": row.get("dividend_yield") or 0.0,
+        }
+    if syms:
+        out = {s: out.get(s, {}) for s in syms if s in out}
+    return out
diff --git a/frontend/src/App.vue b/frontend/src/App.vue
index a8b0657..74c595a 100644
--- a/frontend/src/App.vue
+++ b/frontend/src/App.vue
@@ -11,6 +11,14 @@ const simCapital = ref(1000000)
 const selectedSymbol = ref(null)
 const symbolDetail = ref(null)
 const symbolLoading = ref(false)
+// backtest
+const btStart = ref('2024-06-01')
+const btEnd = ref('2026-06-01')
+const btCapital = ref(1000000)
+const btFreq = ref('monthly')
+const btLoading = ref(false)
+const btResult = ref(null)
+const btRuns = ref([])
 const simMode = ref('backtest')
 const simLoading = ref(false)
 const simResult = ref(null)
@@ -310,6 +318,31 @@ function closeSymbolDetail() {
   symbolDetail.value = null
 }
 
+async function runBacktest() {
+  btLoading.value = true
+  btResult.value = null
+  try {
+    btResult.value = await fetchJson('/api/v1/backtest', {
+      method: 'POST',
+      headers: { 'Content-Type': 'application/json' },
+      body: JSON.stringify({
+        start: btStart.value, end: btEnd.value,
+        capital: Number(btCapital.value), freq: btFreq.value,
+      }),
+    })
+    await loadBacktestRuns()
+  } catch (caught) {
+    btResult.value = { error: caught.message }
+  } finally {
+    btLoading.value = false
+  }
+}
+async function loadBacktestRuns() {
+  try { btRuns.value = (await fetchJson('/api/v1/backtest/runs')).runs || [] }
+  catch { btRuns.value = [] }
+}
+const pnlClass = (net) => net != null ? (net >= 0 ? 'positive-text' : 'negative-text') : ''
+
 async function unlockPaper() {
   if (!paperToken.value) {
     notice.value = 'Enter the paper-session token to unlock paper recording.'
@@ -371,7 +404,7 @@ async function recordPaperEntry() {
   }
 }
 
-onMounted(loadDashboard)
+onMounted(async () => { await loadDashboard(); await loadBacktestRuns() })
 </script>
 
 <template>
@@ -636,6 +669,61 @@ onMounted(loadDashboard)
           <div v-if="!simResult" class="empty-research">กด 'คำนวณการจัดสรร' เพื่อดูว่า 50/20/30 จัดสรรทุนของคุณไปที่หุ้นไหนบ้าง</div>
         </section>
 
+        <section class="panel backtest-panel" id="backtest">
+          <div class="panel-header signal-header">
+            <div>
+              <div class="section-kicker">การย้อนทดสอบ</div>
+              <h2>Backtest (ย้อนทดสอบ)</h2>
+              <p class="panel-subtitle">กำหนดช่วงวัน แล้วระบบจัดสรร 50/20/30 ณ วันที่เริ่ม ลงทุนและถือจนถึงวันสิ้นสุด — สรุปกำไร/ขาดทุนจากราคา + เงินปันผล.</p>
+            </div>
+          </div>
+          <div class="backtest-controls">
+            <label>ตั้งแต่ <input type="date" v-model="btStart" /></label>
+            <label>ถึง <input type="date" v-model="btEnd" /></label>
+            <label>ทุน <input type="number" v-model.number="btCapital" step="100000" /></label>
+            <label>ความถี่
+              <select v-model="btFreq">
+                <option value="monthly">รายเดือน</option>
+                <option value="quarterly">รายไตรมาส</option>
+              </select>
+            </label>
+            <button class="primary-btn" :disabled="btLoading" @click="runBacktest">{{ btLoading ? 'กำลังย้อนทดสอบ…' : 'รัน Backtest' }}</button>
+          </div>
+
+          <div v-if="btResult?.error" class="state-card error-state">{{ btResult.error }}</div>
+          <div v-else-if="btResult" class="backtest-results">
+            <div class="bt-kpi-grid">
+              <div class="bt-kpi"><span>กำไรจากราคา</span><strong :class="pnlClass(btResult.price_pnl)">{{ formatNumber(btResult.price_pnl) }} บาท</strong></div>
+              <div class="bt-kpi"><span>เงินปันผล</span><strong class="positive-text">{{ formatNumber(btResult.dividend_income) }} บาท</strong></div>
+              <div class="bt-kpi"><span>มูลค่าสุดท้าย</span><strong>{{ formatNumber(btResult.final_value) }} บาท</strong></div>
+              <div class="bt-kpi"><span>ผลตอบแทนสุทธิ</span><strong :class="pnlClass(btResult.net_return)">{{ (btResult.net_return * 100).toFixed(2) }}%</strong></div>
+            </div>
+            <div class="bt-meta muted-cell">Trades: {{ btResult.trades }} · ช่วง {{ btResult.start }} → {{ btResult.end }}</div>
+            <div v-if="Object.keys(btResult.holdings || {}).length" class="bt-holdings">
+              <strong>พอร์ตสุดท้าย:</strong>
+              <span v-for="(qty, sym) in btResult.holdings" :key="sym" class="theme-tag">{{ sym }} {{ qty }} หุ้น</span>
+            </div>
+          </div>
+          <div v-else class="empty-research">กำหนดช่วงวันแล้วกด 'รัน Backtest' เพื่อดูผล (กำไร/ขาดทุนจากราคา + ปันผล)</div>
+
+          <div v-if="btRuns.length" class="bt-history">
+            <div class="section-kicker">ประวัติการย้อนทดสอบ</div>
+            <table class="source-table">
+              <thead><tr><th>#</th><th>ช่วง</th><th>ทุน</th><th>กำไรราคา</th><th>ปันผล</th><th>ผลตอบแทน</th><th>รันเมื่อ</th></tr></thead>
+              <tbody>
+                <tr v-for="r in btRuns.slice().reverse()" :key="r.id">
+                  <td>{{ r.id }}</td><td>{{ r.start }} → {{ r.end }}</td>
+                  <td>{{ formatNumber(r.capital) }}</td>
+                  <td :class="pnlClass(r.price_pnl)">{{ formatNumber(r.price_pnl) }}</td>
+                  <td class="positive-text">{{ formatNumber(r.dividend_income) }}</td>
+                  <td :class="pnlClass(r.net_return)">{{ (r.net_return * 100).toFixed(2) }}%</td>
+                  <td class="muted-cell">{{ r.ran_at ? formatDate(r.ran_at) : '—' }}</td>
+                </tr>
+              </tbody>
+            </table>
+          </div>
+        </section>
+
         <!-- 05 / บันทึกการวิเคราะห์ removed per user (redundant with theme-panel narratives) -->
       </template>
     </main>
diff --git a/frontend/src/style.css b/frontend/src/style.css
index d516999..6687991 100644
--- a/frontend/src/style.css
+++ b/frontend/src/style.css
@@ -189,6 +189,21 @@ tbody tr:hover { background: rgba(255,255,255,.025); }
 .calc-step-note { font-size: 11px; color: var(--faint); margin-top: 3px; line-height: 1.5; }
 .calc-z { font-size: 11px; color: var(--faint); margin-top: 8px; line-height: 1.6; }
 
+/* backtest section */
+.backtest-controls { display: flex; flex-wrap: wrap; gap: 12px; align-items: flex-end; padding: 16px 0; }
+.backtest-controls label { display: flex; flex-direction: column; gap: 4px; font-size: 11px; color: var(--faint); }
+.backtest-controls input, .backtest-controls select { background: #0a0e14; border: 1px solid var(--line-bright); color: var(--text); border-radius: 6px; padding: 7px 9px; font-size: 12px; }
+.primary-btn { background: var(--mint); color: #062a1f; border: none; border-radius: 7px; padding: 9px 16px; font-weight: 700; cursor: pointer; font-size: 12px; }
+.primary-btn:disabled { opacity: .5; cursor: not-allowed; }
+.bt-kpi-grid { display: grid; grid-template-columns: repeat(4, 1fr); gap: 10px; margin: 12px 0; }
+.bt-kpi { background: rgba(255,255,255,.03); border: 1px solid var(--line-bright); border-radius: 8px; padding: 12px; }
+.bt-kpi span { display: block; font-size: 11px; color: var(--faint); margin-bottom: 6px; }
+.bt-kpi strong { font-size: 15px; font-family: 'DM Mono', monospace; }
+.bt-meta { margin: 4px 0 10px; font-size: 11px; }
+.bt-holdings { margin-top: 8px; font-size: 12px; color: var(--text-2); display: flex; flex-wrap: wrap; gap: 6px; align-items: center; }
+.bt-history { margin-top: 20px; }
+.bt-history .source-table td { font-size: 12px; padding: 6px 8px; }
+
 .thesis-list { display: flex; flex-direction: column; gap: 10px; margin: 12px 0; }
 .thesis-row { display: flex; gap: 10px; align-items: baseline; padding-bottom: 8px; border-bottom: 1px solid var(--line-weak, rgba(255,255,255,.05)); }
 .thesis-theme { min-width: 130px; color: var(--accent); }