options-payoff

# Options Payoff Curve Skill

Generates a fully interactive HTML widget (via `visualize:show_widget`) showing:
- **Expiry payoff curve** (dashed gray line) — intrinsic value at expiration
- **Theoretical value curve** (solid colored line) — Black-Scholes price at current DTE/IV
- Dynamic sliders for all key parameters
- Real-time stats: max profit, max loss, breakevens, current P&L at spot

---

## Step 1: Extract Strategy From User Input

When the user provides a screenshot or text, extract:

| Field | Where to find it | Default if missing |
|---|---|---|
| Strategy type | Title bar / leg description | "custom" |
| Underlying | Ticker symbol | SPX |
| Strike(s) | K1, K2, K3... in title or leg table | nearest round number |
| Premium paid/received | Filled price or avg price | 5.00 |
| Quantity | Position size | 1 |
| Multiplier | 100 for equity options, 100 for SPX | 100 |
| Expiry | Date in title | 30 DTE |
| Spot price | Current underlying price (NOT strike) | middle strike |
| IV | Shown in greeks panel, or estimate from vega | 20% |
| Risk-free rate | — | 4.3% |

**Critical for screenshots**: The spot price is the CURRENT price of the underlying index/stock, NOT the strikes. Never default spot to a strike price value.

**Current SPX reference price:**
```
!`python3 -c "import yfinance as yf; print(f'SPX ≈ {yf.Ticker(\"^GSPC\").fast_info[\"lastPrice\"]:.0f}')" 2>/dev/null || echo "SPX price unavailable — check market data"`
```

---

## Step 2: Identify Strategy Type

Match to one of the supported strategies below, then read the corresponding section in `references/strategies.md`.

| Strategy | Legs | Key Identifiers |
|---|---|---|
| **butterfly** | Buy K1, Sell 2×K2, Buy K3 | 3 strikes, "Butterfly" in title |
| **vertical_spread** | Buy K1, Sell K2 (same expiry) | 2 strikes, debit or credit |
| **calendar_spread** | Buy far-expiry K, Sell near-expiry K | Same strike, 2 expiries |
| **iron_condor** | Sell K2/K3, Buy K1/K4 wings | 4 strikes, 2 spreads |
| **straddle** | Buy Call K + Buy Put K | Same strike, both types |
| **strangle** | Buy OTM Call + Buy OTM Put | 2 strikes, both OTM |
| **covered_call** | Long 100 shares + Sell Call K | Stock + short call |
| **naked_put** | Sell Put K | Single leg |
| **ratio_spread** | Buy 1×K1, Sell N×K2 | Unequal quantities |

For strategies not listed, use `custom` mode: decompose into individual legs and sum their P&Ls.

---

## Step 3: Compute Payoffs

### Black-Scholes Put Price
```
d1 = (ln(S/K) + (r + σ²/2)·T) / (σ·√T)
d2 = d1 - σ·√T
put = K·e^(-rT)·N(-d2) - S·N(-d1)
```

### Black-Scholes Call Price (via put-call parity)
```
call = put + S - K·e^(-rT)
```

### Butterfly Put Payoff (expiry)
```
if S >= K3: 0
if S >= K2: K3 - S
if S >= K1: S - K1
else: 0
```
Net P&L per share = payoff − premium_paid

### Vertical Spread (call debit) Payoff (expiry)
```
long_call = max(S - K1, 0)
short_call = max(S - K2, 0)
payoff = long_call - short_call - net_debit
```

### Calendar Spread Theoretical Value
Calendar cannot be expressed as a simple expiry function — always use BS pricing for both legs:
```
value = BS(S, K, T_far, r, IV_far) - BS(S, K, T_near, r, IV_near)
```
For expiry curve of calendar: near leg expires worthless, far leg = BS with remaining T.

### Iron Condor Payoff (expiry)
```
put_spread = max(K2-S, 0) - max(K1-S, 0)   // short put spread
call_spread = max(S-K3, 0) - max(S-K4, 0)  // short call spread
payoff = credit_received - put_spread - call_spread
```

---

## Step 4: Render the Widget

Use `visualize:read_me` with modules `["chart", "interactive"]` before building.

### Required Controls (sliders)

**Structure section:**
- All strike prices (K1, K2, K3... as needed by strategy)
- Premium paid/received
- Quantity
- Multiplier (100 default, show for clarity)

**Pricing variables section:**
- IV % (5–80%, step 0.5)
- DTE — days to expiry (0–90)
- Risk-free rate % (0–8%)

**Spot price:**
- Full-width slider, range = [min_strike - 20%, max_strike + 20%], defaulting to ACTUAL current spot

### Required Stats Cards (live-updating)
- Max profit (expiry)
- Max loss (expiry)
- Breakeven(s) — show both for two-sided strategies
- Current theoretical P&L at spot

### Chart Specs
- X-axis: SPX/underlying price
- Y-axis: Total USD P&L (not per-share)
- Blue solid line = theoretical value at current DTE/IV
- Gray dashed line = expiry payoff
- Green dashed vertical = strike prices (K2 center strike brighter)
- Amber dashed vertical = current spot price
- Fill above zero = green 10% opacity; below zero = red 10% opacity
- Tooltip: show both curves on hover

### Code template

Use this JS structure inside the widget, adapting `pnlExpiry()` and `bfTheory()` per strategy:

```js
// Black-Scholes helpers (always include)
function normCDF(x) { /* Horner approximation */ }
function bsCall(S,K,T,r,sig) { /* standard BS call */ }
function bsPut(S,K,T,r,sig) { /* standard BS put */ }

// Strategy-specific expiry payoff (returns per-share value BEFORE premium)
function expiryValue(S, ...strikes) { ... }

// Strategy-specific theoretical value using BS
function theoreticalValue(S, ...strikes, T, r, iv) { ... }

// Main update() reads all sliders, computes arrays, destroys+recreates Chart.js instance
function update() { ... }

// Attach listeners
['k1','k2',...,'iv','dte','rate','spot'].forEach(id => {
  document.getElementById(id).addEventListener('input', update);
});
update();
```

---

## Step 5: Respond to User

After rendering the widget, briefly explain:
1. What strategy was detected and how legs were mapped
2. Max profit / max loss at current settings
3. One key insight (e.g., "spot is currently 950 pts below the profit zone, expiring tomorrow")

Keep it concise — the chart speaks for itself.

---

## Reference Files

- `references/strategies.md` — Detailed payoff formulas and edge cases for each strategy type
- `references/bs_code.md` — Copy-paste ready Black-Scholes JS implementation with normCDF

Read the relevant reference file if you're unsure