Duolingo gives you points for completing lessons that you can trade in for streak freezes. A streak freeze costs 200 points (IIRC), and you seem to normally get ~5-10 points per day that you complete a lesson (closer to 5 or 6 on average, it seems a little random). But basically it seems like you earn enough points to buy a streak freeze every month or so.
Duolingo gives you points for completing lessons that you can trade in for streak freezes. A streak freeze costs 200 points (IIRC), and you seem to normally get ~5-10 points per day that you complete a lesson (closer to 5 or 6 on average, it seems a little random). But basically it seems like you earn enough points to buy a streak freeze every month or so.