Option Strategies

Follow these steps to implement the short put calendar spread strategy:

1. In the Initializeinitialize method, set the start date, end date, cash, and Option universe.
Select Language: C#Python

private Symbol _symbol;

public override void Initialize()
{
    SetStartDate(2017, 2, 1);
    SetEndDate(2017, 2, 19);
    SetCash(500000);

    UniverseSettings.Asynchronous = true;
    var option = AddOption("GOOG", Resolution.Minute);
    _symbol = option.Symbol;
    option.SetFilter(universe => universe.IncludeWeeklys().PutCalendarSpread(0, 30, 60));
}

def initialize(self) -> None:
    self.set_start_date(2017, 2, 1)
    self.set_end_date(2017, 2, 19)
    self.set_cash(500000)

    self.universe_settings.asynchronous = True
    option = self.add_option("GOOG", Resolution.MINUTE)
    self._symbol = option.symbol
    option.set_filter(lambda universe: universe.include_weeklys().put_calendar_spread(0, 30, 60))

The PutCalendarSpreadput_calendar_spread filter narrows the universe down to just the two contracts you need to form a short put calendar spread.

2. In the OnDataon_data method, select the strike price and expiration dates of the contracts in the strategy legs.
Select Language: C#Python

public override void OnData(Slice slice)
{
    if (Portfolio.Invested ||
        !slice.OptionChains.TryGetValue(_symbol, out var chain))
    {
        return;
    }

    // Get the ATM strike
    var atmStrike = chain.OrderBy(x => Math.Abs(x.Strike - chain.Underlying.Price)).First().Strike;

    // Select the ATM put Option contracts
    var puts = chain.Where(x => x.Strike == atmStrike && x.Right == OptionRight.Put);
    if (puts.Count() == 0) return;

    // Select the near and far expiry contracts
    var expiries = puts.Select(x => x.Expiry).ToList();
    var nearExpiry = expiries.Min();
    var farExpiry = expiries.Max();

def on_data(self, slice: Slice) -> None:
    if self.portfolio.invested:
        return

    # Get the OptionChain
    chain = slice.option_chains.get(self._symbol, None)
    if not chain:
        return

    # Get the ATM strike
    atm_strike = sorted(chain, key=lambda x: abs(x.strike - chain.underlying.price))[0].strike

    # Select the ATM put Option contracts
    puts = [i for i in chain if i.strike == atm_strike and i.right == OptionRight.PUT]
    if len(puts) == 0:
        return

    # Select the near and far expiry dates
    expiries = sorted([x.expiry for x in puts])
    near_expiry = expiries[0]
    far_expiry = expiries[-1]

3. In the OnDataon_data method, select the contracts and place the orders.

Approach A: Call the OptionStrategies.ShortPutCalendarSpreadOptionStrategies.short_put_calendar_spread method with the details of each leg and then pass the result to the Buybuy method.

Select Language: C#Python

var optionStrategy = OptionStrategies.ShortPutCalendarSpread(_symbol, atmStrike, nearExpiry, farExpiry);
Buy(optionStrategy, 1);

option_strategy = OptionStrategies.short_put_calendar_spread(self._symbol, atm_strike, near_expiry, far_expiry)
self.buy(option_strategy, 1)

Approach B: Create a list of Leg objects and then call the Combo Market Ordercombo_market_order, Combo Limit Ordercombo_limit_order, or Combo Leg Limit Ordercombo_leg_limit_order method.

Select Language: C#Python

var nearExpiryPut = puts.Single(x => x.Expiry == nearExpiry);
var farExpiryPut = puts.Single(x => x.Expiry == farExpiry);

var legs = new List<Leg>()
    {
        Leg.Create(nearExpiryPut.Symbol, 1),
        Leg.Create(farExpiryPut.Symbol, -1)
    };
ComboMarketOrder(legs, 1);

near_expiry_put = [x for x in puts if x.expiry == near_expiry][0]
far_expiry_put = [x for x in puts if x.expiry == far_expiry][0]

legs = [
    Leg.create(near_expiry_put.symbol, 1),
    Leg.create(far_expiry_put.symbol, -1)
]
self.combo_market_order(legs, 1)

The short put calendar spread is a limited-reward-limited-risk strategy. The payoff is taken at the shorter-term expiration. The payoff is

$$\begin{array}{rcll} P^{\textrm{short-term}}_T & = & (K - S_T)^{+}\\ P_T & = & (P^{\textrm{short-term}}_T - P^{\textrm{long-term}}_T + P^{\textrm{long-term}}_0 - P^{\textrm{short-term}}_0)\times m - fee \end{array}$$ $$\begin{array}{rcll} \textrm{where} & P^{\textrm{short-term}}_T & = & \textrm{Shorter term put value at time T}\\ & P^{\textrm{long-term}}_T & = & \textrm{Longer term put value at time T}\\ & S_T & = & \textrm{Underlying asset price at time T}\\ & K & = & \textrm{Strike price}\\ & P_T & = & \textrm{Payout total at time T}\\ & P^{\textrm{short-term}}_0 & = & \textrm{Shorter term put value at position opening (debit paid)}\\ & P^{\textrm{long-term}}_0 & = & \textrm{Longer term put value at position opening (credit received)}\\ & m & = & \textrm{Contract multiplier}\\ & T & = & \textrm{Time of shorter term put expiration} \end{array}$$

The following chart shows the payoff at expiration:

The maximum profit is the net credit received, $P^{\textrm{long-term}}_0 - P^{\textrm{short-term}}_0$. It occurs when the underlying price moves very deep ITM or OTM so the values of both puts are close to zero.

The maximum loss is undetermined because it depends on the underlying volatility. It occurs when $S_T = S_0$ and the spread of the 2 puts are at their maximum.

If the Option is American Option, there is a risk of early assignment on the contract you sell. Additionally, if you don't close the put positions together, the naked short put will have unlimited drawdown risk after the long put expires.