Plankalkül (German pronunciation: [ˈplaːnkalkyːl]) is a programming language designed for engineering purposes by Konrad Zuse between 1942 and 1945. It was the first high-level programming language to be designed for a computer. Zuse never implemented Plankalkül on any of his Z-series machines.

Kalkül (from Latin calculus) is the German term for a formal system—as in Hilbert-Kalkül, the original name for the Hilbert-style deduction system—so Plankalkül refers to a formal system for planning.

In the domain of creating computing machines, Zuse was self-taught, and developed them without knowledge about other mechanical computing machines that existed already – although later on (building the Z3) being inspired by Hilbert's and Ackermann's book on elementary mathematical logic (see Principles of Mathematical Logic). To describe logical circuits, Zuse invented his own diagram and notation system, which he called "combinatorics of conditionals" (German: Bedingungskombinatorik). After finishing the Z1 in 1938, Zuse discovered that the calculus he had independently devised already existed and was known as propositional calculus. What Zuse had in mind, however, needed to be much more powerful (propositional calculus is not Turing-complete and is not able to describe even simple arithmetic calculations). In May 1939, he described his plans for the development of what would become Plankalkül. He wrote the following in his notebook:

Seit etwa einem halben Jahr allmähliches Einführen in die formale Logik. Viele meiner früheren Gedanken habe ich dort wiedergefunden. (Bedingungskombinatorik = Aussagenlogik; Lehre von den Intervallen = Gebietenkalkül). Ich plane jetzt die Aufsetzung des 'Plankalküls'. Hierzu sind eine Reihe von Begriffen zu klären.

Almost half a year of gradual introduction into formal logic. I rediscovered there lots of my previous thoughts. (combinatorics of conditionals = propositional calculus; study of intervals = lattice theory). I now plan the adoption of "Calculus of plans" onto this. A series of concepts need to be clarified for this.

While working on his doctoral dissertation, Zuse developed the first known formal system of algorithm notation capable of handling branches and loops. In 1942 he began writing a chess program in Plankalkül. In 1944, Zuse met with the German logician and philosopher Heinrich Scholz, who expressed appreciation for Zuse's utilization of logical calculus. In 1945, Zuse described Plankalkül in an unpublished book. The collapse of Nazi Germany, however, prevented him from submitting his manuscript.

At that time the only two working computers in the world were ENIAC and Harvard Mark I, neither of which used a compiler, and ENIAC needed to be reprogrammed for each task by changing how the wires were connected.

Although most of his computers were destroyed by Allied bombs, Zuse was able to rescue one machine, the Z4, and move it to the Alpine village of Hinterstein (part of Bad Hindelang).