Additivity of spreads to range value.

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For a given pair of ranges with the same high and low strikes, the sum of payouts of a bull call spread and a bear put spread is equal to the value of the range.

 

When the underlying expires at the high strike of the range or above, the payout of a bull call spread is the range, and the bear put spread payout is zero.

 

When the underlying expires at the low strike of the range or below, the payout of a bear put spread is the range, and the payout of the bull call spreads is zero.

 

Within the range, going from low to high strikes, as the payout of the underlying increases, the payout of bear put spreads starts at the range value, and looses value as the underlying increases. The bull call spread payout increases from zero as the underlying expires above the low strike.. 

 

The sum of payouts for equal strikes bear call spreads and bull put spreads also adds up to the range of the spreads.