Coupon collection expectation calculator

Calculate expected additional draws to complete collection and completion probability within queried additional draws with your own figures.

Your numbers

Use the units shown. Results update as you change valid inputs.

Use expected additional draws to complete collection and completion probability within queried additional draws to compare changes to your inputs. The method and limits below explain the scope.

Examples

Examples

Try the starting example

Equally likely collectible types
5
Distinct types already owned
2
Additional independent draws to query
3
Expected additional draws to complete collection
9.166667
Completion probability within queried additional draws
0.048
Distinct missing types
3
Probability next draw is a currently missing type
0.6

Try another scenario

Equally likely collectible types
5
Distinct types already owned
3
Additional independent draws to query
3
Expected additional draws to complete collection
7.5
Completion probability within queried additional draws
0.192
Distinct missing types
2
Probability next draw is a currently missing type
0.4
Calculation method

Calculation method

Expected additional draws to complete collection

Types×(1+1/2+...+1/missing), zero when complete.

Completion probability within queried additional draws

Exact inclusion–exclusion sum sum((-1)^j×choose(missing,j)×(types−j)^draws)/types^draws.

Distinct missing types

Types−already owned; duplicate owned copies do not change this count.

Probability next draw is a currently missing type

Missing/types before making the next draw; later discovery chances decline as types are found.

Symbols and units
a
Equally likely collectible types
b
Distinct types already owned
c
Additional independent draws to query

Use the units shown. A list keeps the order in which you enter its values. The symbol ^ means “raised to the power of”.

Calculation steps and notation

sum(list) adds all entries in the list.

Assumptions & limits

Assumptions & limits

  • Uniform independent draws with replacement, starting with a supplied number of distinct owned types. At most 50 missing types and 500 queried draws; rarity weights, trading and guaranteed-new mechanics are outside this model.
Are these inputs private?

These calculations run in your browser. A shared link contains the values you choose to share. Only questions submitted to the separate AI finder are sent to OpenAI.

Further reading

OpenStax: finite probability and sampling without replacement; rules are explicit in each worksheet ↗

Background reading; this does not imply endorsement or independent review of SumFizz.

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