In Old English, numbers or more specifically numerals are almost all recognizably related to those of Modern English, so they shouldn't be too hard to learn for a Modern English speaker.

Cardinal numbers

Cardinal numbers are the type of number that are used to count and enumerate things, like "one", "two", and "three" in Modern English, as in "there are three pigs".

Cardinal numbers in Old English could either be declined adjectivally in declension agreement with whatever they were referring to, or treated like a noun which would be followed by the genitive plural of whatever they were referring to. The Old English words for 1, 2, and 3 were always treated in the former manner - like an adjective that modified a noun or a pronoun. Here are the declensions of these cardinal numerals:

Note that the declension pattern for "ān" is exactly the same as the strong adjectival declension.

Note that those three numerals were always declined the same way - never in the weak declension, except that the word "ān" did occur in the weak declension; but it had a slightly different meaning to just straight "one".

The words for 4 through to 19 were normally not declined when used like an adjective, but when used as a substantive they were usually declined like a strong noun, according to their gender and case.

The words for these numbers are:

• fēoƿer - four
• fīf - five
• seox, six - six
• seofon - seven
• eahta - eight
• nigon - nine
• tīen - ten
• endleofan - eleven
• tƿelf - twelve
• þrēotīne - thirteen
• fēoƿertīne - fourteen
• fīftīne - fifteen
• sixtīne- sixteen
• seofontīne - seventeen
• eahtatīne - eighteen
• nigontīne - nineteen

The words for the "decades" (20, 30, 40, etc.) were:

• tƿentiġ - twenty
• þrītiġ - thirty
• fēoƿertiġ - forty
• fīftiġ - fifty
• sixtiġ - sixty
• hundseofontiġ - seventy
• hundeahtiġ - eighty
• hundnigontiġ - ninety
• hundtēontiġ - hundred, "teenty"
• hundendleofantiġ - hundred and ten, "eleventy" (as seen in J. R. R. Tolkien's The Lord of the Rings)
• hundtƿelftiġ - hundred and twenty, "twelfty" (twelvety)

Note that from "seventy" onwards, the decade words are prefixed with "hund-".

In Old English, the words for "hundred", "hundred and ten", and "hundred and twenty"˝were also treated like decade words.

Ordinal numbers

Ordinal numbers are numbers that are used to rank things in a particular order, like Modern English "first", "second", and "third". All ordinal number forms were always declined like the weak adjectival declension, except for the word "ōðer" - "second", which was always declined like the strong adjectival declension.

In Modern English, for most numbers, we just add the suffix "-th" to the cardinal form of the number to form an ordinal, as in "nine" - "ninth". Similarly, in Old English, the normal basic suffix to form ordinal forms from cardinal numbers was '-þa', but sometimes it varied slightly.

The ordinals for the numbers 1 to 3 were formed unpredictably. They were:

• forma - first
• ōðer - second (compare Modern English "other")
• þridda - third

The ordinals for some of the rest of the "under-twenties" are not always fully predictable. They are:

• fēorða - fourth
• fīfta - fifth
• sixta - sixth
• seofoða - seventh (note that "n" disappeared before the "-þa" suffix)
• eahtoða - eighth
• nigoða - ninth (same thing happens as with "seofoða")
• tēoða - tenth (compare the Modern English word "tithe" - also, same thing as with "seofoða")
• endleofta - eleventh
• tƿelfta - twelfth
• þrēotēoða - thirteenth (the word "þrēo" plus the word "tēoða"
• fēoƿertēoða - fourteenth
• fīftēoða - fifteenth
• sixtēoða - sixteenth
• seofontēoða - seventeenth
• eahtatēoða - eighteenth
• nigontēoða - nineteenth

The ordinals for the decades are easily formed just by adding the suffix "-oða" to the normal cardinal form, always. Like this:

• tƿentigoða - twentieth
• þrītigoða - thirtieth
• fēoƿertigoða - fortieth
• fiftigoða - fiftieth
• sixtigoða - sixtieth
• hundseofontigoða - seventieth
• hundeahtatigoða - eightieth
• hundnigontigoða - ninetieth
• hundteontigoða - hundred/teentieth
• hundendleofantiġoða - hundred and ten/eleventieth
• hundtƿelftiġoða - hundred and twenty/twelftieth