diff --git a/Cargo.toml b/Cargo.toml
index cae0d90..30fbd12 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -2,7 +2,7 @@
 resolver = "2"
 
 members = [
-  "leptos_webpage",
+  "leptos_webpage", "session_iter",
 ]
 
 [profile]
diff --git a/leptos_webpage/Cargo.toml b/leptos_webpage/Cargo.toml
index 3e7bfff..255443c 100644
--- a/leptos_webpage/Cargo.toml
+++ b/leptos_webpage/Cargo.toml
@@ -13,4 +13,5 @@ leptos = { version = "0.7", features = ["csr"] }
 console_error_panic_hook = "0.1.7"
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
-clap = { version = "4.5", features = ["derive"] }
\ No newline at end of file
+clap = { version = "4.5", features = ["derive"] }
+session_iter = { path = "../session_iter"}
\ No newline at end of file
diff --git a/leptos_webpage/src/session.rs b/leptos_webpage/src/session.rs
index 8351433..1f86678 100644
--- a/leptos_webpage/src/session.rs
+++ b/leptos_webpage/src/session.rs
@@ -3,22 +3,6 @@ use chrono::NaiveDate;
 use serde::{Deserialize, Serialize};
 use std::collections::HashMap;
 
-#[derive(Debug, Clone, Eq, PartialEq, Serialize, Deserialize)]
-pub struct OldDatedSession {
-  pub day: Day,
-  pub session: Session,
-  pub applying_exception: Option<Exception>,
-}
-
-impl Noted for OldDatedSession {
-  fn get_note(&self) -> Option<&String> {
-    match &self.applying_exception {
-      Some(e) => e.get_note(),
-      None => self.session.get_note(),
-    }
-  }
-}
-
 #[derive(Debug, Clone, Eq, PartialEq, Serialize, Deserialize)]
 pub enum DatedSession {
   Regular {
diff --git a/session_iter/Cargo.toml b/session_iter/Cargo.toml
new file mode 100644
index 0000000..59e1ac1
--- /dev/null
+++ b/session_iter/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "session_iter"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+chrono = { version = "0.4", features = ["serde"] }
+serde = { version = "1.0", features = ["derive"] }
+clap = { version = "4.5", features = ["derive"] }
\ No newline at end of file
diff --git a/session_iter/src/day.rs b/session_iter/src/day.rs
new file mode 100644
index 0000000..4db6ced
--- /dev/null
+++ b/session_iter/src/day.rs
@@ -0,0 +1,49 @@
+use chrono::{Datelike, Local, NaiveDate, Weekday};
+use serde::{Deserialize, Serialize};
+use std::ops::Deref;
+
+#[derive(Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash, Serialize, Deserialize)]
+#[repr(transparent)]
+pub struct Day {
+  date: NaiveDate,
+}
+
+impl From<NaiveDate> for Day {
+  fn from(date: NaiveDate) -> Self {
+    Self { date }
+  }
+}
+
+impl Default for Day {
+  fn default() -> Self {
+    Self::from(Local::now().date_naive())
+  }
+}
+
+impl Day {
+  pub fn date(&self) -> NaiveDate {
+    self.date
+  }
+
+  pub fn weekday(&self) -> Weekday {
+    self.date.weekday()
+  }
+
+  pub fn weekday_of_month(&self) -> u8 {
+    self.date.day0() as u8 / 7 + 1
+  }
+}
+
+impl Deref for Day {
+  type Target = NaiveDate;
+
+  fn deref(&self) -> &Self::Target {
+    &self.date
+  }
+}
+
+impl From<Day> for NaiveDate {
+  fn from(day: Day) -> Self {
+    day.date
+  }
+}
\ No newline at end of file
diff --git a/session_iter/src/lib.rs b/session_iter/src/lib.rs
new file mode 100644
index 0000000..e884830
--- /dev/null
+++ b/session_iter/src/lib.rs
@@ -0,0 +1,5 @@
+pub mod day;
+pub mod session;
+#[cfg(test)]
+mod test_util;
+
diff --git a/session_iter/src/main.rs b/session_iter/src/main.rs
new file mode 100644
index 0000000..e71fdf5
--- /dev/null
+++ b/session_iter/src/main.rs
@@ -0,0 +1 @@
+fn main() {}
\ No newline at end of file
diff --git a/session_iter/src/session.rs b/session_iter/src/session.rs
new file mode 100644
index 0000000..51134a4
--- /dev/null
+++ b/session_iter/src/session.rs
@@ -0,0 +1,187 @@
+pub mod iter;
+pub mod rule;
+
+use crate::day::Day;
+use crate::session::rule::{SessionRule, SessionRuleLike, WeekdayOfMonth};
+use chrono::NaiveDate;
+use serde::{Deserialize, Serialize};
+use std::collections::BTreeMap;
+
+type Note = Option<String>;
+
+macro_rules! impl_opt_noted {
+  ($ty: ident) => {
+    impl OptNoted for $ty {
+      fn note(&self) -> Option<&str> {
+        self.note.as_ref().map(String::as_str)
+      }
+    }
+  };
+  ($ty: ident with $($variant: ident),+) => {
+    impl OptNoted for $ty {
+      fn note(&self) -> Option<&str> {
+        match self {
+          $(Self::$variant(opt_noted) => opt_noted.note(),)+
+        }
+      }
+    }
+  };
+}
+
+macro_rules! impl_with_note {
+  ($ty: ident) => {
+    impl WithNote for $ty {
+      fn with_note(self, note: &str) -> Self {
+        #[allow(clippy::needless_update)]
+        Self {
+          note: Some(note.to_owned()),
+          ..self
+        }
+      }
+    }
+  };
+}
+
+macro_rules! impl_from {
+  ($what: ident for $ty: ident by $intermediate: ident) => {
+    impl From<$what> for $ty {
+      fn from(value: $what) -> Self {
+        Self::from($intermediate::from(value))
+      }
+    }
+  };
+  ($what: ident for $ty: ident as $variant: ident) => {
+    impl From<$what> for $ty {
+      fn from(value: $what) -> Self {
+        Self::$variant(value)
+      }
+    }
+  };
+  ($what: ident for $ty: ident) => {
+    impl_from!($what for $ty as $what);
+  };
+}
+
+#[derive(Debug, Clone, Eq, PartialEq, Hash, Serialize, Deserialize)]
+pub enum Session {
+  Regular(RegularSession),
+  Extra(ExtraSession),
+}
+
+impl_from!(RegularSession for Session as Regular);
+impl_from!(ExtraSession for Session as Extra);
+
+#[derive(Debug, Clone, Eq, PartialEq, Hash, Serialize, Deserialize)]
+pub struct RegularSession {
+  pub rule: SessionRule,
+  pub note: Note,
+  pub except: BTreeMap<Day, Except>,
+}
+
+impl From<SessionRule> for RegularSession {
+  fn from(rule: SessionRule) -> Self {
+    Self {
+      rule,
+      note: None,
+      except: Default::default(),
+    }
+  }
+}
+
+impl RegularSession {
+  pub fn except<D, E>(mut self, day: D, except: E) -> Self
+  where
+    D: Into<Day>,
+    E: Into<Except>,
+  {
+    self.except.insert(day.into(), except.into());
+    self
+  }
+
+  pub fn next_regular_session_day<D>(&self, current_date: D) -> Option<Day>
+  where
+    D: Into<Day>,
+  {
+    self
+      .rule
+      .to_session_day_iter(current_date)
+      .find(|day| !self.except.contains_key(day))
+  }
+}
+
+impl_from!(WeekdayOfMonth for RegularSession by SessionRule);
+impl_opt_noted!(RegularSession);
+impl_with_note!(RegularSession);
+
+#[derive(Debug, Clone, Eq, PartialEq, Ord, PartialOrd, Hash, Serialize, Deserialize)]
+pub struct ExtraSession {
+  pub day: Day,
+  pub note: Note,
+}
+
+impl From<Day> for ExtraSession {
+  fn from(day: Day) -> Self {
+    Self { day, note: None }
+  }
+}
+
+impl_from!(NaiveDate for ExtraSession by Day);
+impl_opt_noted!(ExtraSession);
+impl_with_note!(ExtraSession);
+
+impl Dated for ExtraSession {
+  fn day(&self) -> Day {
+    self.day
+  }
+}
+
+#[derive(Debug, Clone, Eq, PartialEq, Hash, Serialize, Deserialize)]
+pub enum Except {
+  Alternation(Alternation),
+  Cancellation(Cancellation),
+}
+
+impl_from!(Alternation for Except);
+impl_from!(Cancellation for Except);
+impl_opt_noted!(Except with Alternation, Cancellation);
+
+#[derive(Debug, Clone, Eq, PartialEq, Hash, Default, Serialize, Deserialize)]
+pub struct Alternation {
+  pub note: Note,
+  pub day: Option<Day>,
+}
+
+impl From<Day> for Alternation {
+  fn from(day: Day) -> Self {
+    Self {
+      day: Some(day),
+      ..Default::default()
+    }
+  }
+}
+
+impl_from!(NaiveDate for Alternation by Day);
+impl_opt_noted!(Alternation);
+impl_with_note!(Alternation);
+
+#[derive(Debug, Clone, Eq, PartialEq, Hash, Default, Serialize, Deserialize)]
+#[serde(default)]
+pub struct Cancellation {
+  pub note: Note,
+}
+
+impl_opt_noted!(Cancellation);
+impl_with_note!(Cancellation);
+
+pub trait Dated {
+  /// The day when this should show up in a calendar
+  fn day(&self) -> Day;
+}
+
+pub trait OptNoted {
+  fn note(&self) -> Option<&str>;
+}
+
+pub trait WithNote {
+  fn with_note(self, note: &str) -> Self;
+}
diff --git a/session_iter/src/session/iter.rs b/session_iter/src/session/iter.rs
new file mode 100644
index 0000000..addcaef
--- /dev/null
+++ b/session_iter/src/session/iter.rs
@@ -0,0 +1,123 @@
+use crate::day::Day;
+use crate::session::{
+  Alternation, Cancellation, Dated, Except, ExtraSession, OptNoted, RegularSession, Session,
+};
+use serde::{Deserialize, Serialize};
+use std::collections::BTreeMap;
+use std::hash::Hash;
+
+#[derive(Debug, Clone)]
+pub struct DatedSessionIter {
+  current_date: Day,
+  sessions: BTreeMap<Day, Vec<DatedSession>>,
+}
+
+impl DatedSessionIter {
+  pub fn new<D, S>(start_date: D, sessions: S) -> DatedSessionIter
+  where
+    D: Into<Day>,
+    S: IntoIterator<Item = Session>,
+  {
+    let current_date = start_date.into();
+
+    //map every session and their exceptions to a date when they should show up in the calendar
+    let sessions =
+      sessions
+        .into_iter()
+        .flat_map(|session| match session {
+          Session::Regular(session) => session
+            .except
+            .iter()
+            .filter(|(&day, _)| current_date <= day)
+            .map(|(&day, except)| match except {
+              Except::Alternation(alternation) => DatedSession::Altered {
+                day: alternation.day.unwrap_or(day),
+                regular: session.clone(),
+                cause: alternation.clone(),
+              },
+              Except::Cancellation(cancellation) => DatedSession::Canceled {
+                day,
+                regular: session.clone(),
+                cause: cancellation.clone(),
+              },
+            })
+            .chain(session.next_regular_session_day(current_date).map(|day| {
+              DatedSession::Regular {
+                day,
+                session: session.clone(),
+              }
+            }))
+            .collect(),
+          Session::Extra(extra) => {
+            //filter out old extra sessions
+            if current_date <= extra.day() {
+              vec![extra.into()]
+            } else {
+              vec![]
+            }
+          }
+        })
+        .fold(BTreeMap::<_, Vec<_>>::new(), |mut map, dated_session| {
+          map
+            .entry(dated_session.day())
+            .or_default()
+            .push(dated_session);
+          map
+        });
+
+    Self {
+      current_date,
+      sessions,
+    }
+  }
+}
+
+//TODO iter implementation for DatedSessionIter
+
+#[derive(Debug, Clone, Eq, PartialEq, Hash, Serialize, Deserialize)]
+pub enum DatedSession {
+  Regular {
+    day: Day,
+    session: RegularSession,
+  },
+  Extra(ExtraSession),
+  Canceled {
+    day: Day,
+    regular: RegularSession,
+    cause: Cancellation,
+  },
+  Altered {
+    ///the day when the regular session would have applied
+    day: Day,
+    regular: RegularSession,
+    cause: Alternation,
+  },
+}
+
+impl From<ExtraSession> for DatedSession {
+  fn from(value: ExtraSession) -> Self {
+    Self::Extra(value)
+  }
+}
+
+impl Dated for DatedSession {
+  fn day(&self) -> Day {
+    match *self {
+      DatedSession::Regular { day, .. } => day,
+      DatedSession::Extra(ref extra) => extra.day(),
+      DatedSession::Canceled { day, .. } => day,
+      DatedSession::Altered { day, ref cause, .. } => cause.day.unwrap_or(day),
+    }
+  }
+}
+
+impl OptNoted for DatedSession {
+  fn note(&self) -> Option<&str> {
+    match self {
+      DatedSession::Regular { session, .. } => session.note(),
+      DatedSession::Extra(extra) => extra.note(),
+      DatedSession::Canceled { cause, .. } => cause.note(),
+      DatedSession::Altered { cause, .. } => cause.note(),
+    }
+  }
+}
diff --git a/session_iter/src/session/rule.rs b/session_iter/src/session/rule.rs
new file mode 100644
index 0000000..8ac0490
--- /dev/null
+++ b/session_iter/src/session/rule.rs
@@ -0,0 +1,149 @@
+use crate::day::Day;
+use chrono::{Datelike, Months, NaiveDate, Weekday};
+use serde::{Deserialize, Serialize};
+use std::ops::Deref;
+
+#[derive(Debug, Clone, Eq, PartialEq, Hash, Serialize, Deserialize)]
+pub enum SessionRule {
+  WeekdayOfMonth(WeekdayOfMonth),
+}
+
+impl From<WeekdayOfMonth> for SessionRule {
+  fn from(value: WeekdayOfMonth) -> Self {
+    Self::WeekdayOfMonth(value)
+  }
+}
+
+impl SessionRule {
+  pub fn to_session_day_iter<D>(&self, start_date: D) -> SessionDayIter<&Self>
+  where
+    D: Into<Day>,
+  {
+    SessionDayIter {
+      rule: self,
+      current_date: Some(start_date.into()),
+    }
+  }
+}
+
+impl SessionRuleLike for SessionRule {
+  fn determine_next_date(&self, current_date: Day) -> Option<Day> {
+    match self {
+      SessionRule::WeekdayOfMonth(weekday_of_month) => {
+        weekday_of_month.determine_next_date(current_date)
+      }
+    }
+  }
+
+  fn accepts(&self, day: Day) -> bool {
+    match self {
+      SessionRule::WeekdayOfMonth(weekday_of_month) => weekday_of_month.accepts(day),
+    }
+  }
+}
+
+#[derive(Debug, Clone)]
+pub struct SessionDayIter<R> {
+  pub rule: R,
+  pub current_date: Option<Day>,
+}
+
+impl<R> Iterator for SessionDayIter<R>
+where
+  R: Deref<Target = SessionRule>,
+{
+  type Item = Day;
+
+  fn next(&mut self) -> Option<Self::Item> {
+    self.current_date = self
+      .current_date
+      .and_then(|date| self.rule.determine_next_date(date));
+    self.current_date
+  }
+}
+
+impl<R> SessionDayIter<R>
+where
+  R: Deref<Target = SessionRule>,
+{
+  pub fn to_owned(&self) -> SessionDayIter<SessionRule> {
+    SessionDayIter {
+      rule: self.rule.clone(),
+      current_date: self.current_date,
+    }
+  }
+}
+
+#[derive(Debug, Copy, Clone, Eq, PartialEq, Hash, Serialize, Deserialize)]
+pub struct WeekdayOfMonth {
+  pub n: u8,
+  pub weekday: Weekday,
+}
+
+impl WeekdayOfMonth {
+  pub fn new(n: u8, weekday: Weekday) -> Self {
+    Self { n, weekday }
+  }
+}
+
+impl SessionRuleLike for WeekdayOfMonth {
+  fn determine_next_date(&self, current_date: Day) -> Option<Day> {
+    let session_this_month = NaiveDate::from_weekday_of_month_opt(
+      current_date.year(),
+      current_date.month(),
+      self.weekday,
+      self.n,
+    )?;
+
+    let date = if session_this_month >= current_date.date() {
+      session_this_month
+    } else {
+      let session_next_month = current_date.checked_add_months(Months::new(1))?;
+      NaiveDate::from_weekday_of_month_opt(
+        session_next_month.year(),
+        session_next_month.month(),
+        self.weekday,
+        self.n,
+      )?
+    };
+
+    Some(date.into())
+  }
+
+  fn accepts(&self, day: Day) -> bool {
+    day.weekday() == self.weekday && day.weekday_of_month() == self.n
+  }
+}
+
+pub trait SessionRuleLike {
+  /// Determines the next session date in form of a [Day], possibly including the `start_date`.
+  fn determine_next_date(&self, current_date: Day) -> Option<Day>;
+
+  /// Whether this rule would be able to produce the given `day`.
+  fn accepts(&self, day: Day) -> bool;
+}
+
+#[cfg(test)]
+mod test_weekday_of_month {
+  use crate::session::rule::{SessionRuleLike, WeekdayOfMonth};
+  use crate::test_util::day;
+  use chrono::Weekday;
+
+  #[test]
+  fn test_next_date() {
+    let rule = WeekdayOfMonth::new(3, Weekday::Tue);
+
+    assert_eq!(
+      rule.determine_next_date(day(17, 2, 2025)),
+      Some(day(18, 2, 2025))
+    );
+    assert_eq!(
+      rule.determine_next_date(day(18, 2, 2025)),
+      Some(day(18, 2, 2025))
+    );
+    assert_eq!(
+      rule.determine_next_date(day(19, 2, 2025)),
+      Some(day(18, 3, 2025))
+    );
+  }
+}
diff --git a/session_iter/src/test_util.rs b/session_iter/src/test_util.rs
new file mode 100644
index 0000000..9261d54
--- /dev/null
+++ b/session_iter/src/test_util.rs
@@ -0,0 +1,10 @@
+use crate::day::Day;
+use chrono::NaiveDate;
+
+pub fn date(day: u32, month: u32, year: i32) -> NaiveDate {
+  NaiveDate::from_ymd_opt(year, month, day).expect("valid date")
+}
+
+pub fn day(day: u32, month: u32, year: i32) -> Day {
+  date(day, month, year).into()
+}
\ No newline at end of file