April to May and September to October. Those are the sweet spots: milder heat, fewer rainy days, and noticeably fewer people than the summer peak. Weekdays inside those windows are quieter still.
What the other months give you
- January and February, highs around 33 °C and lows near 22 °C, with the heaviest crowds of the year, because Argentine families are on holiday
- March, still hot at about 32 °C, but the holiday crowds have gone home
- June to August, the mild season, highs of 24 to 27 °C, and August has the fewest rainy days of any month
- Late October, November and December, the wettest months, and therefore the fullest falls. More water, more local visitors, a few more days you will get rained on
There is no bad month. The park works year-round and the falls flow year-round. The worst case in summer is that you get wet, which is welcome in that heat, and Devil’s Throat and the boat ride soak you regardless of the forecast.
For a one-day trip specifically
The month matters less than you would expect. What decides whether the day works is the flight pair, an early departure and a late return. That is a scheduling question, not a seasonal one. Pick the month that suits the rest of your trip, then pick the flights carefully.
