kalkulieren
to calculate
To calculate the costs or price of something, often in a business context.
Der Handwerker hat die Kosten für die Renovierung genau kalkuliert.
The tradesman calculated the costs for the renovation precisely.

to calculate
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to calculate
To calculate the costs or price of something, often in a business context.
Der Handwerker hat die Kosten für die Renovierung genau kalkuliert.
The tradesman calculated the costs for the renovation precisely.

The word 'kalkulieren' (to calculate) comes from the Latin 'calculus', which means 'small stone'. In the past, people used little stones for counting. So the basic meaning is always 'to do arithmetic' or 'to calculate'.
Der Architekt kalkuliert die Materialmenge für den Bau.
The architect calculates the amount of material for the construction.
'Kalkulieren' (to calculate) can mean both a concrete mathematical calculation and an abstract, strategic consideration. When it is about numbers, it is concrete. When it is about risks or possibilities, it is abstract.
Er kalkulierte die Gewinnchancen, bevor er investierte.
He calculated the chances of making a profit before he invested.
In a business context, 'kalkulieren' (to calculate) is often combined with financial terms. Typical objects are 'die Kosten' (the costs), 'den Preis' (the price), 'ein Angebot' (an offer/quote), or 'das Budget' (the budget).
Das Unternehmen muss seine Preise neu kalkulieren, um wettbewerbsfähig zu bleiben.
The company has to recalculate its prices in order to remain competitive.
In the meaning 'to take something into account', 'kalkulieren' (to calculate) is often used with the preposition 'mit' (with) and the dative. You calculate 'mit' a possibility or a risk.
Bei der Projektplanung müssen wir mit unvorhergesehenen Problemen kalkulieren.
When planning the project, we have to reckon with unforeseen problems.
to calculate / to expect
'rechnen' and 'kalkulieren' can both have to do with numbers or with planning. 'rechnen' is the normal, general word: you solve problems or expect something, for example 'mit Regen rechnen' (to expect rain). 'kalkulieren' often sounds more objective and is used especially for costs, prices, and planning. It can also mean deliberately including a possibility in a plan. Learners may confuse the words because both can mean 'mit etwas rechnen' (to reckon with / expect something). In everyday language, 'rechnen' is usually more natural; for prices and projects, 'kalkulieren' often is.

Für das Fest kalkuliert das Team die Kosten sehr genau.
For the festival, the team is calculating the costs very precisely.
Wir rechnen morgen mit starkem Verkehr.
We expect heavy traffic tomorrow.