Finnish uses postpositions to express when something happened in the past ("ago") or will happen in the future ("in"). These require the preceding time period to take specific noun cases.
Future Time: kuluttua and päästä ("In / After")
To say something will happen "in" or "after" a certain amount of time, use kuluttua or päästä (these are interchangeable). Both require the preceding time period—including any numbers—to be in the genitive case (-n).
| The move is in two weeks. | Muutto on kahden viikon kuluttua. |
| In three years he will graduate from high school. | Kolmen vuoden päästä hän valmistuu lukiosta. |
Past Time: sitten ("Ago")
To say something happened a certain amount of time "ago," use sitten. The time amount before sitten does not take the genitive:
- A single unit of time stays in the nominative (the basic dictionary form, like vuosi).
- For amounts greater than one, the number stays nominative, and the time word takes the partitive (e.g., kaksi vuotta), following standard Finnish number rules.
| The firstborn was born a year ago. | Esikoinen syntyi vuosi sitten. |
| They started dating two years ago. | He alkoivat seurustella kaksi vuotta sitten. |
Comparing the Cases
When discussing life events, pay close attention to whether you are looking backward or forward in time. Notice how even a single unit of time (vuosi) changes to the genitive (vuoden) before kuluttua or päästä, but stays nominative before sitten.
| The maternity leave starts in a week. | Äitiysloma alkaa viikon päästä. |
| The child will become an adult and move away in a year. | Lapsi aikuistuu ja muuttaa pois vuoden kuluttua. |
| The divorce happened a year ago, and I returned to the childhood home. | Ero tapahtui vuosi sitten, ja minä palasin lapsuudenkotiin. |
