How French counts from 70 to 99 in sixties and twenties
Up to 69, French numbers work much like English ones: soixante is sixty and soixante-cinq is sixty-five. After that, standard French stops inventing new tens. Seventy is soixante-dix, literally sixty-ten. Eighty is quatre-vingts, four twenties. Ninety is quatre-vingt-dix, four twenties and ten. This is an old way of counting in twenties that survives in modern French.
English speakers trip over this because English gives every ten its own word: seventy, eighty, ninety. In French you have to do a quick sum in your head. When you hear quatre-vingt-dix-sept, you have to work out that it means 4 × 20 + 10 + 7 = 97. The good news is that the system is completely regular once you see it. Belgium and Switzerland also use simpler words, septante, huitante and nonante, which you will meet when you travel.
Think of the numbers from 60 to 99 as two blocks of twenty.
Start from soixante and keep counting past ten. You get soixante-dix (70), soixante et onze (71), soixante-douze (72) and so on, all the way to soixante-dix-neuf (79).
Start from quatre-vingts and do the same. You get quatre-vingt-un (81) up to quatre-vingt-dix (90), then quatre-vingt-onze (91) up to quatre-vingt-dix-neuf (99).
The key is that the teen words onze, douze, treize, quatorze, quinze and seize come back in the 70s and 90s. So 75 is not sixty-ten-five but soixante-quinze, sixty-fifteen. From 77 onwards you use dix-sept, dix-huit and dix-neuf, just as you do after ten.
Rule of thumb: take the last digit of the tens, and if it is 7 or 9, add a teen number to the block below. For 7 you use soixante and for 9 you use quatre-vingt.
soixante is the base for the whole 70s. It is an ordinary number on its own.
soixante-dix is seventy. Its neighbours swap the dix for a teen number.
quatre-vingts is eighty, four twenties. It starts the second block.
quatre-vingt-dix is ninety. The 90s follow the same teen pattern as the 70s.
In Belgium and Switzerland, people use septante (70) and nonante (90). In some Swiss cantons, such as Vaud, Valais and Fribourg, they also use huitante (80). These work exactly like soixante or cinquante: septante-cinq is 75 and nonante-sept is 97. Belgians say quatre-vingts for 80. The h of huitante is aspirated like the one in huit, so there is no liaison before it.
You should understand these words, but in France stick to the standard forms. Speakers there understand septante and nonante, but they sound Belgian or Swiss.
French adds et only before un and onze in 21, 31, 41, 51, 61 and 71, as in trente et un and soixante et onze. The eighty block never takes it, so you say quatre-vingt-un and quatre-vingt-onze.
Traditional spelling joins the parts with hyphens except around et. Since the 1990 spelling reform, you can also hyphenate everything, as in soixante-et-onze. Both are accepted.
It disappears when another number follows, as in quatre-vingt-trois. This is covered in its own article.
French reads them in pairs, so 06 78 92 is zéro six, soixante-dix-huit, quatre-vingt-douze. Practise hearing these quickly.
In standard French, the 70s are built on soixante and the 80s and 90s on quatre-vingts, four twenties. For 70 to 79 and 90 to 99, add a number from dix to dix-neuf to the block below: soixante-quinze is 75 and quatre-vingt-dix-sept is 97. Use et only in soixante et onze, never in the eighties or nineties. In Belgium and Switzerland, septante, huitante and nonante replace the arithmetic.