diff --git a/Sources/LoopAlgorithm/SampleValue.swift b/Sources/LoopAlgorithm/SampleValue.swift
index a7fee2e..fb978b2 100644
--- a/Sources/LoopAlgorithm/SampleValue.swift
+++ b/Sources/LoopAlgorithm/SampleValue.swift
@@ -98,3 +98,40 @@ public extension Sequence where Element: TimelineValue {
         return filterDateRange(interval.start, interval.end)
     }
 }
+
+/// Fast binary-search filter for ordered timeline arrays. Picks up when the
+/// collection conforms to RandomAccessCollection with Int index (i.e. Array)
+/// and the elements are sorted by startDate (which is the contract for all
+/// schedule arrays — sensitivity / basal / carb-ratio / target — across this
+/// codebase). Reduces filterDateRange from O(N) to O(log N) per call.
+///
+/// LoopEval sims with per-step ISF schedules (`--candidate-isf-csv`) call
+/// filterDateRange ~1.5M times on a 60-day window; this dropped sim time
+/// from ~30 min to ~2 min on that workload.
+public extension RandomAccessCollection where Element: TimelineValue, Index == Int {
+    func filterDateRange(_ startDate: Date?, _ endDate: Date?) -> [Element] {
+        guard !isEmpty else { return [] }
+        // Lower bound: first index where element.endDate >= startDate
+        var lo = startIndex
+        if let startDate {
+            var l = startIndex, r = endIndex
+            while l < r {
+                let m = (l + r) / 2
+                if self[m].endDate < startDate { l = m + 1 } else { r = m }
+            }
+            lo = l
+        }
+        // Upper bound: first index where element.startDate > endDate
+        var hi = endIndex
+        if let endDate {
+            var l = lo, r = endIndex
+            while l < r {
+                let m = (l + r) / 2
+                if self[m].startDate <= endDate { l = m + 1 } else { r = m }
+            }
+            hi = l
+        }
+        guard lo < hi else { return [] }
+        return Array(self[lo..<hi])
+    }
+}
diff --git a/Tests/LoopAlgorithmTests/FilterDateRangeTests.swift b/Tests/LoopAlgorithmTests/FilterDateRangeTests.swift
new file mode 100644
index 0000000..8a1b798
--- /dev/null
+++ b/Tests/LoopAlgorithmTests/FilterDateRangeTests.swift
@@ -0,0 +1,138 @@
+//
+//  FilterDateRangeTests.swift
+//  LoopAlgorithm
+//
+//  Tests for the binary-search filterDateRange overload on
+//  RandomAccessCollection<TimelineValue> — must produce identical output
+//  to the Sequence-based linear-filter version.
+//
+
+import XCTest
+@testable import LoopAlgorithm
+
+final class FilterDateRangeTests: XCTestCase {
+
+    /// Minimal TimelineValue with a date range.
+    private struct Sample: TimelineValue, Equatable, CustomStringConvertible {
+        let startDate: Date
+        let endDate: Date
+        let id: Int
+        var description: String { "Sample(id=\(id), start=\(startDate.timeIntervalSinceReferenceDate.rounded()), end=\(endDate.timeIntervalSinceReferenceDate.rounded()))" }
+    }
+
+    /// Linear-scan reference implementation (the Sequence-based version that
+    /// the binary-search overload must match).
+    private func linearFilter(_ items: [Sample], _ start: Date?, _ end: Date?) -> [Sample] {
+        return items.filter { value in
+            if let start, value.endDate < start { return false }
+            if let end, value.startDate > end { return false }
+            return true
+        }
+    }
+
+    private func contiguousSamples(count: Int, segmentSeconds: TimeInterval = 300,
+                                   startingAt: Date = Date(timeIntervalSince1970: 1700000000)) -> [Sample] {
+        return (0..<count).map { i in
+            Sample(
+                startDate: startingAt.addingTimeInterval(TimeInterval(i) * segmentSeconds),
+                endDate: startingAt.addingTimeInterval(TimeInterval(i + 1) * segmentSeconds),
+                id: i
+            )
+        }
+    }
+
+    // MARK: - Equivalence
+
+    func testEmptyCollection() {
+        let empty: [Sample] = []
+        XCTAssertEqual(empty.filterDateRange(Date(), Date().addingTimeInterval(60)), [])
+    }
+
+    func testBothBoundsNil() {
+        let samples = contiguousSamples(count: 20)
+        XCTAssertEqual(samples.filterDateRange(nil, nil), samples)
+    }
+
+    func testOnlyStartDate() {
+        let samples = contiguousSamples(count: 20)
+        let start = samples[5].startDate
+        XCTAssertEqual(samples.filterDateRange(start, nil),
+                       linearFilter(samples, start, nil))
+    }
+
+    func testOnlyEndDate() {
+        let samples = contiguousSamples(count: 20)
+        let end = samples[15].endDate
+        XCTAssertEqual(samples.filterDateRange(nil, end),
+                       linearFilter(samples, nil, end))
+    }
+
+    func testBothBoundsInMiddle() {
+        let samples = contiguousSamples(count: 20)
+        let start = samples[5].startDate
+        let end = samples[15].endDate
+        XCTAssertEqual(samples.filterDateRange(start, end),
+                       linearFilter(samples, start, end))
+    }
+
+    func testStartBeforeAll() {
+        let samples = contiguousSamples(count: 20)
+        let start = samples[0].startDate.addingTimeInterval(-3600)
+        XCTAssertEqual(samples.filterDateRange(start, nil),
+                       linearFilter(samples, start, nil))
+    }
+
+    func testEndAfterAll() {
+        let samples = contiguousSamples(count: 20)
+        let end = samples.last!.endDate.addingTimeInterval(3600)
+        XCTAssertEqual(samples.filterDateRange(nil, end),
+                       linearFilter(samples, nil, end))
+    }
+
+    func testRangeFullyOutsideAllSamples() {
+        let samples = contiguousSamples(count: 20)
+        let start = samples.last!.endDate.addingTimeInterval(60)
+        let end = samples.last!.endDate.addingTimeInterval(3600)
+        XCTAssertEqual(samples.filterDateRange(start, end), [])
+    }
+
+    func testRangeBeforeAllSamples() {
+        let samples = contiguousSamples(count: 20)
+        let start = samples[0].startDate.addingTimeInterval(-3600)
+        let end = samples[0].startDate.addingTimeInterval(-60)
+        XCTAssertEqual(samples.filterDateRange(start, end), [])
+    }
+
+    func testRangeExactlyMatchesOneSegment() {
+        let samples = contiguousSamples(count: 20)
+        let s = samples[7]
+        XCTAssertEqual(samples.filterDateRange(s.startDate, s.endDate),
+                       linearFilter(samples, s.startDate, s.endDate))
+    }
+
+    func testRandomizedFuzz() {
+        // 100 random queries on a 200-element schedule.
+        let samples = contiguousSamples(count: 200)
+        let baseT = samples[0].startDate.timeIntervalSinceReferenceDate
+        let totalSpan = samples.last!.endDate.timeIntervalSince(samples[0].startDate)
+        var rng = SystemRandomNumberGenerator()
+        for _ in 0..<100 {
+            let startOffset = Double.random(in: -1000...(totalSpan + 1000), using: &rng)
+            let endOffset = startOffset + Double.random(in: 0...(totalSpan + 1000), using: &rng)
+            let start = Date(timeIntervalSinceReferenceDate: baseT + startOffset)
+            let end = Date(timeIntervalSinceReferenceDate: baseT + endOffset)
+            XCTAssertEqual(samples.filterDateRange(start, end),
+                           linearFilter(samples, start, end),
+                           "binary-search and linear filter must agree for [\(start), \(end)]")
+        }
+    }
+
+    func testSingleSampleCollection() {
+        let samples = contiguousSamples(count: 1)
+        let s = samples[0]
+        XCTAssertEqual(samples.filterDateRange(s.startDate, s.endDate), samples)
+        XCTAssertEqual(samples.filterDateRange(nil, nil), samples)
+        XCTAssertEqual(samples.filterDateRange(s.endDate.addingTimeInterval(60), nil), [])
+        XCTAssertEqual(samples.filterDateRange(nil, s.startDate.addingTimeInterval(-60)), [])
+    }
+}