HealthKit

Read and write health and fitness data from the Apple Health store. Covers authorization, queries, writing samples, background delivery, and workout sessions. Targets Swift 6.3 / iOS 26+.

Contents

• Setup and Availability
• Authorization
• Reading Data: Sample Queries
• Reading Data: Statistics Queries
• Reading Data: Statistics Collection Queries
• Writing Data
• Background Delivery
• Workout Sessions
• Common Data Types
• HKUnit Reference
• Common Mistakes
• Review Checklist
• References

Setup and Availability

Project Configuration

1. Enable the HealthKit capability in Xcode (adds the entitlement)
2. Add NSHealthShareUsageDescription (read) and NSHealthUpdateUsageDescription (write) to Info.plist
3. For background delivery, enable the "Background Delivery" sub-capability

Availability Check

Always check availability before accessing HealthKit. iPad and some devices do not support it.

import HealthKit

let healthStore = HKHealthStore()

guard HKHealthStore.isHealthDataAvailable() else {
    // HealthKit not available on this device (e.g., iPad)
    return
}

Create a single HKHealthStore instance and reuse it throughout your app. It is thread-safe.

Authorization

Request only the types your app genuinely needs. App Review rejects apps that over-request.

func requestAuthorization() async throws {
    let typesToShare: Set<HKSampleType> = [
        HKQuantityType(.stepCount),
        HKQuantityType(.activeEnergyBurned)
    ]

    let typesToRead: Set<HKObjectType> = [
        HKQuantityType(.stepCount),
        HKQuantityType(.heartRate),
        HKQuantityType(.activeEnergyBurned),
        HKCharacteristicType(.dateOfBirth)
    ]

    try await healthStore.requestAuthorization(
        toShare: typesToShare,
        read: typesToRead
    )
}

Checking Authorization Status

The app can only determine if it has not yet requested authorization. If the user denied access, HealthKit returns empty results rather than an error -- this is a privacy design.

let status = healthStore.authorizationStatus(
    for: HKQuantityType(.stepCount)
)

switch status {
case .notDetermined:
    // Haven't requested yet -- safe to call requestAuthorization
    break
case .sharingAuthorized:
    // User granted write access
    break
case .sharingDenied:
    // User denied write access (read denial is indistinguishable from "no data")
    break
@unknown default:
    break
}

Reading Data: Sample Queries

Use HKSampleQueryDescriptor (async/await) for one-shot reads. Prefer descriptors over the older callback-based HKSampleQuery.

func fetchRecentHeartRates() async throws -> [HKQuantitySample] {
    let heartRateType = HKQuantityType(.heartRate)

    let descriptor = HKSampleQueryDescriptor(
        predicates: [.quantitySample(type: heartRateType)],
        sortDescriptors: [SortDescriptor(\.endDate, order: .reverse)],
        limit: 20
    )

    let results = try await descriptor.result(for: healthStore)
    return results
}

// Extracting values from samples:
for sample in results {
    let bpm = sample.quantity.doubleValue(
        for: HKUnit.count().unitDivided(by: .minute())
    )
    print("\(bpm) bpm at \(sample.endDate)")
}

Reading Data: Statistics Queries

Use HKStatisticsQueryDescriptor for aggregated single-value stats (sum, average, min, max).

func fetchTodayStepCount() async throws -> Double? {
    let calendar = Calendar.current
    let startOfDay = calendar.startOfDay(for: Date())
    let endOfDay = calendar.date(byAdding: .day, value: 1, to: startOfDay)!

    let predicate = HKQuery.predicateForSamples(
        withStart: startOfDay, end: endOfDay
    )
    let stepType = HKQuantityType(.stepCount)
    let samplePredicate = HKSamplePredicate.quantitySample(
        type: stepType, predicate: predicate
    )

    let query = HKStatisticsQueryDescriptor(
        predicate: samplePredicate,
        options: .cumulativeSum
    )

    let result = try await query.result(for: healthStore)
    return result?.sumQuantity()?.doubleValue(for: .count())
}

Options by data type:

• Cumulative types (steps, calories): .cumulativeSum
• Discrete types (heart rate, weight): .discreteAverage, .discreteMin, .discreteMax

Reading Data: Statistics Collection Queries

Use HKStatisticsCollectionQueryDescriptor for time-series data grouped into intervals -- ideal for charts.

func fetchDailySteps(forLast days: Int) async throws -> [(date: Date, steps: Double)] {
    let calendar = Calendar.current
    let endDate = calendar.startOfDay(
        for: calendar.date(byAdding: .day, value: 1, to: Date())!
    )
    let startDate = calendar.date(byAdding: .day, value: -days, to: endDate)!