diff --git a/Cargo.toml b/Cargo.toml
index 602206a..e79cbdb 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -12,4 +12,4 @@ reqwest = { version = "^0.12", features = ["json"] }
 serde = { version = "^1.0", features = ["derive"] }
 thiserror = "^2.0"
 tokio = { version = "^1.42", features = ["full"] }
-time = { version = "^0.3", features = ["serde", "parsing", "formatting", "macros"] }
+time = { version = "^0.3", features = ["serde", "parsing", "formatting"]}
diff --git a/examples/demo.rs b/examples/demo.rs
index d6290c1..5a815ac 100644
--- a/examples/demo.rs
+++ b/examples/demo.rs
@@ -1,7 +1,7 @@
-use beeminder::types::CreateDatapoint;
+use beeminder::types::{CreateDatapoint, UpdateDatapoint};
 use beeminder::BeeminderClient;
 use std::env;
-use time::macros::datetime;
+use time::{Duration, OffsetDateTime};
 
 #[tokio::main]
 async fn main() {
@@ -14,22 +14,44 @@ async fn main() {
         Err(e) => println!("{e:#?}"),
     }
 
-    let since = datetime!(2024-12-13 20:00 UTC);
+    let since = OffsetDateTime::now_utc() - Duration::days(2);
     match client.get_user_diff(since).await {
         Ok(user) => println!("{user:#?}"),
         Err(e) => println!("{e:#?}"),
     }
 
-    match client.get_datapoints("meditation", None, Some(2)).await {
-        Ok(datapoints) => println!("{datapoints:#?}"),
-        Err(e) => println!("{e:#?}"),
-    }
-
-    let d = CreateDatapoint::new(1.0)
-        .with_comment("Test #hashtag datapoint")
-        .with_requestid("unique-id-42");
-    match client.create_datapoint("meditation", &d).await {
+    let new_datapoint = CreateDatapoint::new(20.0)
+        .with_comment("I did some pushups!")
+        .with_requestid("unique-pushup-id-42");
+    match client.create_datapoint("pushups", &new_datapoint).await {
         Ok(datapoint) => println!("Added: {datapoint:#?}"),
         Err(e) => println!("{e:#?}"),
     }
+
+    let goal_name = "pushups";
+    match client.get_datapoints(&goal_name, None, Some(3)).await {
+        Ok(datapoints) => {
+            if let Some(first_datapoint) = datapoints.first() {
+                let update_datapoint = UpdateDatapoint::from(first_datapoint)
+                    .with_value(40.0)
+                    .with_comment("Much better.");
+
+                match client.update_datapoint(&goal_name, &update_datapoint).await {
+                    Ok(datapoint) => println!("Updated: {datapoint:#?}"),
+                    Err(e) => println!("Update error: {e:#?}"),
+                }
+
+                match client
+                    .delete_datapoint(&goal_name, &update_datapoint.id)
+                    .await
+                {
+                    Ok(datapoint) => println!("Deleted: {datapoint:#?}"),
+                    Err(e) => println!("Delete error: {e:#?}"),
+                }
+            } else {
+                println!("No datapoints found");
+            }
+        }
+        Err(e) => println!("Get datapoints error: {e:#?}"),
+    }
 }
diff --git a/src/lib.rs b/src/lib.rs
index 72ad8e2..6379842 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -1,5 +1,7 @@
 pub mod types;
-use crate::types::{CreateDatapoint, Datapoint, GoalSummary, UserInfo, UserInfoDiff};
+use crate::types::{
+    CreateDatapoint, Datapoint, GoalSummary, UpdateDatapoint, UserInfo, UserInfoDiff,
+};
 use reqwest::Client;
 use time::OffsetDateTime;
 
@@ -123,7 +125,37 @@ impl BeeminderClient {
         self.post(&endpoint, datapoint).await
     }
 
-    /// Deletes a specific datapoint for the user's goal.
+    /// Updates an existing datapoint for a goal.
+    ///
+    /// # Arguments
+    /// * `goal` - The slug/name of the goal to update
+    /// * `update` - The datapoint update containing the ID and fields to update
+    ///
+    /// # Errors
+    /// Returns an error if the HTTP request fails or if the response cannot be parsed
+    pub async fn update_datapoint(
+        &self,
+        goal: &str,
+        update: &UpdateDatapoint,
+    ) -> Result<Datapoint, Error> {
+        let endpoint = format!(
+            "users/{}/goals/{}/datapoints/{}.json",
+            self.username, goal, update.id
+        );
+
+        let response = self
+            .client
+            .put(format!("{}{}", self.base_url, endpoint))
+            .query(&[("auth_token", self.api_key.as_str())])
+            .query(update)
+            .send()
+            .await?
+            .error_for_status()?;
+
+        response.json().await.map_err(Error::from)
+    }
+
+    /// Deletes a specific datapoint for a goal.
     ///
     /// # Arguments
     /// * `goal` - The name of the goal.
diff --git a/src/types.rs b/src/types.rs
index a2bcf67..3aefada 100644
--- a/src/types.rs
+++ b/src/types.rs
@@ -171,6 +171,82 @@ impl CreateDatapoint {
     }
 }
 
+/// Parameters for updating an existing datapoint
+#[derive(Debug, Clone, Serialize)]
+pub struct UpdateDatapoint {
+    /// ID of the datapoint to update
+    #[serde(skip_serializing)]
+    pub id: String,
+    /// Optional new timestamp for the datapoint
+    #[serde(
+        with = "time::serde::timestamp::option",
+        skip_serializing_if = "Option::is_none"
+    )]
+    pub timestamp: Option<OffsetDateTime>,
+    /// Optional new value
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub value: Option<f64>,
+    /// Optional new comment
+    #[serde(skip_serializing_if = "Option::is_none")]
+    pub comment: Option<String>,
+}
+
+impl From<&Datapoint> for UpdateDatapoint {
+    fn from(datapoint: &Datapoint) -> Self {
+        Self {
+            id: datapoint.id.clone(),
+            timestamp: Some(datapoint.timestamp),
+            value: Some(datapoint.value),
+            comment: datapoint.comment.clone(),
+        }
+    }
+}
+
+impl UpdateDatapoint {
+    /// Creates an empty update for the given datapoint ID
+    #[must_use]
+    pub fn new(id: impl Into<String>) -> Self {
+        Self {
+            id: id.into(),
+            timestamp: None,
+            value: None,
+            comment: None,
+        }
+    }
+
+    /// Creates an update from an existing datapoint with no changes
+    #[must_use]
+    pub fn from_datapoint(datapoint: &Datapoint) -> Self {
+        Self {
+            id: datapoint.id.clone(),
+            timestamp: Some(datapoint.timestamp),
+            value: Some(datapoint.value),
+            comment: datapoint.comment.clone(),
+        }
+    }
+
+    /// Sets a new timestamp
+    #[must_use]
+    pub fn with_timestamp(mut self, timestamp: OffsetDateTime) -> Self {
+        self.timestamp = Some(timestamp);
+        self
+    }
+
+    /// Sets a new value
+    #[must_use]
+    pub fn with_value(mut self, value: f64) -> Self {
+        self.value = Some(value);
+        self
+    }
+
+    /// Sets a new comment
+    #[must_use]
+    pub fn with_comment(mut self, comment: &str) -> Self {
+        self.comment = Some(comment.to_string());
+        self
+    }
+}
+
 #[derive(Debug, Serialize, Deserialize)]
 pub struct UserInfo {
     /// Username of the Beeminder account