How German numbers work: the teens and the tens

The whole system on one screen

Three colours build every number to 99: the unit, the joining und, and the ten.

Ich bin siebenundvierzig. - I am forty-seven.

The teens: the unit plus zehn

From thirteen to nineteen German does what English does: the unit, then ten.

Two of them lose letters, and these are the classic spelling traps:

• Sie ist sechzehn. - She is sixteen.
• Er ist siebzehn. - He is seventeen.

The dropped s changes the sound too: in sechzehn the ch is the soft ch of ich, not the ks of sechs.

The tens: -zig, and one ß

The tens add -zig to the unit, the same ending as English -ty:

• vierfour
• vierzehnfourteen
• vierzigforty

Three need watching:

• zwanzig (20), not zweizig: two has changed shape. Ich bin zwanzig. - I am twenty.
• dreißig (30) is the only ten that ends in -ßig instead of -zig. Er ist dreißig. - He is thirty.
• sechzig and siebzig shrink exactly like their teens. Sie ist siebzig. - She is seventy.

The -ig at the end is said like the ch in ich in standard German, so zwanzig sounds like tsvan-tsich. In the south, Austria and Switzerland you will hear a k instead. Both are correct.