diff --git a/Cargo.lock b/Cargo.lock
index 2eeb8a2..edec213 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -711,6 +711,7 @@ dependencies = [
  "iced",
  "iced_aw",
  "itertools",
+ "peg",
  "serde",
  "serde_json",
 ]
@@ -1684,6 +1685,33 @@ dependencies = [
  "windows-targets 0.48.5",
 ]
 
+[[package]]
+name = "peg"
+version = "0.8.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "400bcab7d219c38abf8bd7cc2054eb9bbbd4312d66f6a5557d572a203f646f61"
+dependencies = [
+ "peg-macros",
+ "peg-runtime",
+]
+
+[[package]]
+name = "peg-macros"
+version = "0.8.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "46e61cce859b76d19090f62da50a9fe92bab7c2a5f09e183763559a2ac392c90"
+dependencies = [
+ "peg-runtime",
+ "proc-macro2",
+ "quote",
+]
+
+[[package]]
+name = "peg-runtime"
+version = "0.8.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "36bae92c60fa2398ce4678b98b2c4b5a7c61099961ca1fa305aec04a9ad28922"
+
 [[package]]
 name = "percent-encoding"
 version = "2.3.0"
diff --git a/Cargo.toml b/Cargo.toml
index efa75d0..7b9c4be 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -13,5 +13,6 @@ iced_aw = { version = "0.7.0", default-features = false, features = [
 	"card",
 ] }
 itertools = "0.11.0"
+peg = "0.8.2"
 serde = { version = "1.0.192", features = ["derive"] }
 serde_json = "1.0.108"
diff --git a/src/calc.rs b/src/calc.rs
new file mode 100644
index 0000000..a22b2a5
--- /dev/null
+++ b/src/calc.rs
@@ -0,0 +1,82 @@
+peg::parser! {
+    pub grammar calc_parser() for str {
+        rule number() -> f64 = n:$(['0'..='9']+ ("." ['0'..='9']*)?) {? n.parse().or(Err("f64"))}
+
+        rule _ = quiet!{[' ' | '\n' | '\t']*}
+
+        pub rule calc() -> f64 =
+            _ v:precedence!{
+                "-" _ x:(@) { std::ops::Neg::neg(x) }
+                "+" _ x:(@) { x }
+                --
+                x:(@) _ "+" _ y:@ { x + y }
+                x:(@) _ "-" _ y:@ { x - y }
+                --
+                x:(@) _ "*" _ y:@ { x * y }
+                x:(@) _ "/" _ y:@ { x / y }
+                --
+                n:number() { n }
+                "(" _ e:calc() _ ")" { e }
+            } _ { v }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::calc_parser;
+
+    #[test]
+    fn prefix_plus() {
+        assert_eq!(calc_parser::calc("+1"), Ok(1.));
+    }
+
+    #[test]
+    fn prefix_minus() {
+        assert_eq!(calc_parser::calc("-1"), Ok(-1.));
+    }
+
+    #[test]
+    fn sum() {
+        assert_eq!(calc_parser::calc("1+1"), Ok(2.));
+    }
+
+    #[test]
+    fn prod() {
+        assert_eq!(calc_parser::calc("2*2"), Ok(4.));
+    }
+
+    #[test]
+    fn div() {
+        assert_eq!(calc_parser::calc("6/3"), Ok(2.));
+    }
+
+    #[test]
+    fn sub() {
+        assert_eq!(calc_parser::calc("6-3"), Ok(3.));
+    }
+
+    #[test]
+    fn literal() {
+        assert_eq!(calc_parser::calc("2"), Ok(2.));
+        assert_eq!(calc_parser::calc("2."), Ok(2.));
+        assert_eq!(calc_parser::calc("2.0"), Ok(2.));
+    }
+
+    #[test]
+    fn whitespace_infix() {
+        assert_eq!(
+            calc_parser::calc("-   (1+     ( 1 *   3) /    6-1)"),
+            Ok(-0.5)
+        );
+    }
+
+    #[test]
+    fn whitespace_prefix() {
+        assert_eq!(calc_parser::calc("        1+1"), Ok(2.));
+    }
+
+    #[test]
+    fn whitespace_suffix() {
+        assert_eq!(calc_parser::calc("1+1     "), Ok(2.));
+    }
+}
diff --git a/src/main.rs b/src/main.rs
index 3d8d70f..083abcb 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -18,6 +18,8 @@ use serde::{Deserialize, Serialize};
 
 type Element<'a> = iced::Element<'a, Message>;
 
+mod calc;
+
 const TEXT_H1: u16 = 30;
 const TEXT_H2: u16 = 25;
 const TEXT_EMPH1: u16 = 17;