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Calculating the Expected Value of a Gacha (for Consecutive Gacha Runs)

Author: ExpectedValueExecutions: 46107

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This calculator determines the expected number of spins required to obtain a desired item in consecutive gacha draws, such as those found in mobile games.
It displays the results for three different types of consecutive gacha draws.

[No Guaranteed Drop]: A consecutive gacha with no guaranteed drops. All slots have the same drop rate.
[Independent Guaranteed Drop]: A consecutive gacha featuring regular slots and one independent guaranteed slot. The guaranteed slot has a different drop rate than the regular slots and only yields specific items. The drop rate for the guaranteed slot remains constant regardless of the results from the regular slots.
[Dependent Guaranteed]: A gacha with a guaranteed slot where, based on a calculated number of consecutive slots, the drop rate for the remaining slot changes depending on the results of the first (consecutive count - 1) slots.When a guaranteed slot is actually displayed, it is purely for presentation purposes. For example, suppose there is a 10-pull gacha that guarantees an SS-rarity item. If no SS-rarity item appears in the first 9 theoretical slots, an SS-rarity item is guaranteed to appear in the remaining theoretical slot; however, if one does appear, the drop rate for that remaining theoretical slot is the same as usual.When a “guaranteed slot” is actually displayed, one of the SS-rarity items that appeared in the 10 calculated slots will be shown in the actual guaranteed slot.

Probability of Appearance: The probability that the desired item will appear at least once when a single consecutive gacha pull is made
Expected number of gacha pulls: The expected number of consecutive gacha pulls required before the desired item appears at least once
Expected amount spent: The expected amount spent on consecutive gacha pulls before the desired item appears at least once
Expected number of appearances: The expected number of times the desired item appears when performing one consecutive gacha pull
Normal drop rate for desired items p
%
Drop rate p_d when a desired item is the target for confirmation
%Used only for 【Independent Determination】 and 【Dependent Determination】
Normal discharge rate p_R for all items subject to finalization
%Used only for 【Dependent Determination】
Number of consecutive occurrences L
連
Number of Gacha Stones Required for One Consecutive Gacha Pull
個
Number of Gems to Purchase
個
Price of Gems to Purchase
yen
Price per consecutive gacha pull yen
     
Probability of occurrence  %  %  %
Expected Value of Gacha Attempts  Times  Times  Times
Expected Value of the Charge Amount  yen  yen  yen
Expected number of occurrences  Times  Times  Times
*The expected number of consecutive gacha spins required for the desired item to appear at least once is denoted as E_gacha, [Type],
and the expected number of times the desired item appears per consecutive gacha spin is denoted as E_appearance, [Type].
*


When the normal drop rate of the desired item < the drop rate of the desired item when it is a guaranteed drop,
the following holds true for the probability of appearance and the expected number of appearances:
[No Guarantee] < [Dependent Guarantee] < [Independent Guarantee].
On the other hand, for the expected number of spins and the expected amount spent,
[No Guaranteed Drop] > [Dependent Guaranteed Drop] > [Independent Guaranteed Drop]
holds true.

 Price of one consecutive gacha = Number of premium stones per consecutive gacha × Price per premium stone ÷ Number of premium stones purchased

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