WilliamsR — Williams %R

Where the close sits relative to the window’s true high: 0 at the high, −100 at the low. Numerically %K − 100, but read on its own scale. The seeded WilliamsClose uses closes; this is the textbook high-low form.

Signature

WilliamsR(period, on=<source>)

Argument	Type	Required	Notes
period	int Param or literal	Yes	Range lookback. Default 14, bounds 1–400.
on=	symbol	No	Source symbol. Defaults to the trade symbol. Reads high, low, close.

Formula

$$ %R = -100,\frac{\max(H, n) - C}{\max(H, n) - \min(L, n)} $$

Warmup

period bars to a full window; partial before that. A flat window returns −50 (neutral).

Reading the value

wr.value
wr < -80
wr.crossed_above(-50)

Example

class WilliamsReversal(Strategy):
    """Buy deep oversold, exit at the midline."""
    period = Param(14, min=1, max=400)
    trade = Symbol()
    sizing = FixedCapital()

    def execute(self):
        wr = WilliamsR(self.period, on=self.trade)
        if wr.value < -80 and self.trade.is_flat:
            self.buy(self.trade, reason=f"%R {wr.value:.0f}")
        if wr.value > -50 and self.trade.is_long:
            self.sell(self.trade, self.trade.position, reason="Midline")

Notes

• Larry Williams’ %R.
• Proven by an assert-via-trade run on SPY daily (matched the formula on every bar; zero alarm trades).
• Single-value on purpose — unlike Stochastic it can be smoothed (SMA(3, on=wr)) and crossed.