diff --git a/src/eval.rs b/src/eval.rs
index 3a36b56..bf6a826 100644
--- a/src/eval.rs
+++ b/src/eval.rs
@@ -7,6 +7,7 @@ use crate::files::commands::{Birthday, Command, File, Note, Spec, Task};
 
 use self::entries::{DateRange, Entry, EntryKind, EntryMap};
 
+mod delta;
 pub mod entries;
 
 #[derive(Debug, thiserror::Error)]
diff --git a/src/eval/delta.rs b/src/eval/delta.rs
new file mode 100644
index 0000000..f2d5095
--- /dev/null
+++ b/src/eval/delta.rs
@@ -0,0 +1,95 @@
+use std::cmp::Ordering;
+
+use crate::files::commands::{Delta, DeltaStep};
+
+impl DeltaStep {
+    fn lower_bound(&self) -> i32 {
+        match self {
+            DeltaStep::Year(n) => {
+                if *n < 0 {
+                    *n * 366
+                } else {
+                    *n * 365
+                }
+            }
+            DeltaStep::Month(n) | DeltaStep::MonthReverse(n) => {
+                if *n < 0 {
+                    *n * 31
+                } else {
+                    *n * 28
+                }
+            }
+            DeltaStep::Day(n) => *n,
+            DeltaStep::Week(n) => *n * 7,
+            DeltaStep::Hour(n) => {
+                if *n < 0 {
+                    *n / 24 + (*n % 24).signum()
+                } else {
+                    *n / 24
+                }
+            }
+            DeltaStep::Minute(n) => {
+                if *n < 0 {
+                    *n / (24 * 60) + (*n % (24 * 60)).signum()
+                } else {
+                    *n / (24 * 60)
+                }
+            }
+            DeltaStep::Weekday(n, _) => match n.cmp(&0) {
+                Ordering::Less => *n * 7 - 1,
+                Ordering::Equal => 0,
+                Ordering::Greater => *n * 7 - 7,
+            },
+        }
+    }
+
+    fn upper_bound(&self) -> i32 {
+        match self {
+            DeltaStep::Year(n) => {
+                if *n > 0 {
+                    *n * 366
+                } else {
+                    *n * 365
+                }
+            }
+            DeltaStep::Month(n) | DeltaStep::MonthReverse(n) => {
+                if *n > 0 {
+                    *n * 31
+                } else {
+                    *n * 28
+                }
+            }
+            DeltaStep::Day(n) => *n,
+            DeltaStep::Week(n) => *n * 7,
+            DeltaStep::Hour(n) => {
+                if *n > 0 {
+                    *n / 24 + (*n % 24).signum()
+                } else {
+                    *n / 24
+                }
+            }
+            DeltaStep::Minute(n) => {
+                if *n > 0 {
+                    *n / (24 * 60) + (*n % (24 * 60)).signum()
+                } else {
+                    *n / (24 * 60)
+                }
+            }
+            DeltaStep::Weekday(n, _) => match n.cmp(&0) {
+                Ordering::Less => *n * 7 - 7,
+                Ordering::Equal => 0,
+                Ordering::Greater => *n * 7 - 1,
+            },
+        }
+    }
+}
+
+impl Delta {
+    pub fn lower_bound(&self) -> i32 {
+        self.0.iter().map(DeltaStep::lower_bound).sum()
+    }
+
+    pub fn upper_bound(&self) -> i32 {
+        self.0.iter().map(DeltaStep::upper_bound).sum()
+    }
+}