Infinity minus 1 equals infinity.

∞ - 1 = ∞

As infinity is not a finite number, so every operation that uses infinity ends up equaling infinity... In reality there is no number prior to infinity, as infinity is a pure concept and not a precise finite number.
Source(s):
http://www59.wolframalpha.com/input/?i=infintiy+-+1
http://mathforum.org/library/drmath/view/64623.html

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∞ - 1 This is the logical number that comes before infinity.
Source(s):
my own deductive logic

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infinity - 1

Infinity is not really a number, just a concept, so the number just before infinity is just an concept as well.
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Start counting, and when you get to infinity it was the number just before that ;). But the biggest number that we have a name for is a googolplex, so you can't count any higher. The reason is because as others said, infinity is not really a number, however, mathematicians are no stranger to using infinity. It can be used in calculations. For example, 1/infinity = 0
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infinity -1 OR

999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999
untill you don't know what to call the next one.. that is the number before infinity

=)
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I was always taught that infinity -1 = infinity. It's a concept, not a number. Since there is no number for infinity, since numbers increase forever and never end, there isn't a number that comes before infinity.
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There does not exist a number which is one less than infinity.
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There is no number before infinity. Infinity is just a concept.
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infinity - 1
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Philosophically speaking, infinity is the point at which you reach when there is no further to go. The spiritualist would call it heaven, the guru would call it Nirvana, and the agnostic would call it bulls--t!

http://www.math.yorku.ca/infinity/Images/newInfinity.jpg

Some would say infinity is a state of mind, a place where one can feel free from the shackles of the world. In that sense, then, the number (or level or whatever) just before that state would be = the state you start in. Once you reach a spiritual plane, for example, then all else outside of it is in the material realm. That way, there exist only two states (or numbers) - infinity, and the one just before it!

Here’s a section from an essay on Infinity by Hector Parr:

“The world of the Pure Mathematician is far removed from the real world. In the real world there is no difficulty finding the length of the diagonal of a square and expressing this as a decimal, but in the perfect world of Pure Mathematics this cannot be done. In the real world we know the process of counting the natural numbers can never be completed, so that the number of numbers is without meaning, while the mathematician finds it necessary to say that if the process were completed, the number would be found to be Aleph-0. These are harmless follies; what the mathematician gets up to inside his ivory tower need not concern those outside.
But the mathematician's ideal world did impinge on reality at the beginning of the twentieth century when Russell (1872-1970) attempted to reduce all mathematical reasoning to simple logic. Even the natural numbers themselves could be defined in terms of a simpler concept, but to make this possible Russell found it necessary to assume that the number of real objects in the universe is itself infinite. Here again I find it astonishing that he made this assumption so glibly. He called the principle his "Axiom of Infinity". Now an "axiom" is something which is self-evident, unlike a "postulate", which is assumed for convenience even though it is not self-evident. Why did Russell not refer to the principle as his "Postulate of Infinity"? To me it is far from self-evident that there are an infinite number of things in the universe; in fact I cannot see that the statement has any meaning. Infinity is an indispensible concept in Pure Mathematics, but is it not meaningless when applied to the number of real things?”
Source(s):
http://meaningofmath.blogspot.com/2005_05_01_archive.html

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There is no number below infinity. Even if you go into what's called the surreal numbers, there is still none because there is still no smallest infinitesimal, so you can't subtract the "smallest thing" from infinity. For example, you might define infinity minus one. But then you can define infinity minus one half.

So there are systems where there is the thing just before infinity. You can add to the real numbers and then stop whenever you feel like it.
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