Swahili has an unusual system of numbers which blends Bantu and Arabic characteristics. See Category:Swahili numerals for a complete list. For more on how certain numbers inflect in Swahili, see Appendix:Swahili noun classes.
The numbers are divided into those that are declinable, and those that are not. The numbers -moja (1), -mbili (2), -tatu (3), -nne (4), -tano (5), and -nane (8) all inflect according to standard patterns, although all except -moja decline only in the plural. All these numbers are derived from Proto-Bantu.
Most higher numbers are from Arabic, and are invariable. There are two words for 9, tisa from Arabic and kenda from Proto-Bantu, but multiples of ten (above the number ten itself) only use Arabic forms (for example, tisini (“ninety”)). However, the highest numbers, like milioni (“million”), come from English (and are invariable as well).
Numbers that are not round are composed of the nearest multiple of ten that is lower than the number in question, plus the remainder. However, if the remainder inflects, it must still agree. For example, "a hundred and two sultans" would be masultani mia na mawili. There are Arabic terms for all the numbers from 11 to 19, but only edashara (“eleven”) and thenashara (“twelve”) see much use.
Two numbers have a special counting form, used only when the number is being treated as an abstract entity. These forms are mosi (“one”) and pili (“two”). These forms are also the ones generally used in dates, as in Januari mosi ("1 January"). All other numbers are morphologically identical when being used as adjectives directly modifying a noun, and as values when counting.
Ordinals are formed by using -a (“of”), which must agree using the verb prefixes with the class of the noun preceding it, followed by the number in question. The two exceptions are -a kwanza (“first”) (kwanza is the infinitive/gerund of -anza (“to begin”)) and -a pili (“second”), which uses the counting form.
Some fractions have special names, generally taken from the Arabic, but those do not follow standard patterns. Otherwise, those with 1 as the numerator are expressed with the n class noun sehemu (“part”) followed by the ordinal of the number in question, so "one-fifth" is "a fifth part". Those with numbers greater than 1 in the numerator are expressed with kwa, saying the denominator followed by the word kwa followed by the numerator.