Daar kun je donder op zeggen

you can be sure of that, you can bet your life on that
[Dutch phrase of the week]
[daar kun je don-der op zeg-gen] 

‘Donder’ is the Dutch noun for ‘thunder’. It is often used as an expletive and today’s phrase is an example of that. It’s however a perfectly normal expression to use, although probably not in formal communication. You can use this expression when you are sure something will happen. Often it implies you are expecting it based on previous experience.

You can also use the expression in the form: “Je kunt er donder op zeggen dat […]”, see the Examples below.

“Als je één klant korting geeft, willen ze allemaal korting; daar kun je donder op zeggen!” 
(“If you give one customer a discount, they all want a discount; you can be sure of that!”)

“Je kunt er donder op zeggen dat als het een paar dagen vriest, er weer over een Elfstedentocht gesproken wordt!” 
(“You can bet your life that when we’ve had a few days of frost, they start talking about an Elfstedentocht again!” Lit.:”…that when it’s freezing for a few days, …” Whenever there are a few consecutive days of frost in winter, the Dutch media start speculating on a potential Elfstedentocht, the last of which was held in 1997.)

“Mijn handbagage is gestolen tijdens het inchecken op Schiphol!” – “Ja, daar kun je donder op zeggen; het is druk, je bent gehaast en gestresst, en dan let je dus niet goed op!” 
(“My hand luggage was stolen during check-in at Schiphol!” – “Yep, that is to be expected; it’s crowded, you are in a hurry and you’re stressed, and that’s when you don’t pay attention properly!” Note the expression ‘binnen de kortste keren’: in no time (at all).)

“Ik was maar 5 minuten weg, kom ik terug bij de auto, heb ik een bon!” – “Daar kun je donder op zeggen, ze controleren in Utrecht aan de lopende band.” 
(“I had only been away for 5 minutes, and when I returned to the car there was a parking ticket waiting for me!” – “That’s bound to happen, they monitor parked cars continuously in Utrecht!”)

“Je kunt er donder op zeggen dat het met een onervaren leraar voor de klas binnen de kortste keren een beestenboel wordt!” 
(“There’s bound to be instant chaos with an unexperienced teacher in the classroom.” Lit.:”… that with an unexperienced teacher in front of the class it will become a hell of a mess in no time!”)

– “Zeer zeker”: most certainly.
– “Zeker weten!”: definitely / for sure!. Lit. “to know for sure.”

“Ga je voetbal kijken vanavond?” – “Zeker weten man, ik wil het voor geen goud missen!”
(“Are you going to watch football/soccer tonight?” – “Definitely man, I wouldn’t want to miss it for the world!” Lit.:”I want to miss it for no gold!”)

Related words:
– Donder: thunder [noun] [de donder, de donders].
– Donderdag: Thursday [noun] [de donderdag, de donderdagen]. Note that we speak of ‘Day of thunder’ as opposed to “Thor‘s Day”.
Zeker: certain, sure [adjective/adverb].
– Geheid: certain, sure [adjective/adverb].
– Verwacht: expected [adjective/adverb].