diff --git a/adapter/src/utils/getBaseUrl.js b/adapter/src/utils/getBaseUrl.js
new file mode 100644
index 00000000..035c7895
--- /dev/null
+++ b/adapter/src/utils/getBaseUrl.js
@@ -0,0 +1,47 @@
+const isUrlAbsolute = (url) => {
+    // the URL constructor will throw for relative URLs
+    try {
+        new URL(url)
+        return true
+    } catch {
+        return false
+    }
+}
+
+/**
+ * Deduces the base URL for the DHIS2 instance from the location at which this
+ * app is hosted. Returns an absolute URL
+ * @param {string} defaultBaseUrl a fallback URL that will be used if the base
+ * URL can't be deduced from the window location
+ * @returns {string} an absolute base URL for the DHIS2 instance
+ */
+export const getBaseUrl = (defaultBaseUrl) => {
+    // if defaultBaseUrl is absolute, use that
+    if (isUrlAbsolute(defaultBaseUrl)) {
+        return defaultBaseUrl
+    }
+
+    const { location } = window
+    const path = location.pathname
+
+    // get penultimate 3 path elements (don't need anything before),
+    // e.g. /dev/api/apps/app-name/index.html => ['api', 'apps', 'app-name'].
+    const splitPath = path.split('/').slice(-4, -1)
+    // could be shorter than 3 elements for e.g. /dhis-web-maps/
+    const l = splitPath.length
+
+    // test for core apps
+    if (/dhis-web-.+/.test(splitPath[l - 1])) {
+        return new URL('..', location.href).href
+    }
+
+    // test for custom apps
+    if (splitPath[l - 3] === 'api' && splitPath[l - 2] === 'apps') {
+        return new URL('../../..', location.href).href
+    }
+
+    // todo: handle path for global shell
+
+    // otherwise, return absolute version of default
+    return new URL(defaultBaseUrl, location.href).href
+}
diff --git a/adapter/src/utils/getBaseUrl.test.js b/adapter/src/utils/getBaseUrl.test.js
new file mode 100644
index 00000000..6f4ec5e3
--- /dev/null
+++ b/adapter/src/utils/getBaseUrl.test.js
@@ -0,0 +1,61 @@
+import { getBaseUrl } from './getBaseUrl.js'
+
+const testOrigin = 'https://debug.dhis2.org'
+// { [testPath]: expectedPath }
+const testPaths = {
+    '/dev/api/apps/simple-app/index.html': '/dev/',
+    '/analytics_dev/dhis-web-maps/plugin.html': '/analytics_dev/',
+    '/dhis-web-line-listing/index.html': '/',
+    '/dhis-web-user-settings/': '/',
+    '/hmis/staging/v41/api/apps/WHO-Data-Quality-App/app.html':
+        '/hmis/staging/v41/',
+}
+
+const windowLocationMock = jest
+    .spyOn(window, 'location', 'get')
+    .mockImplementation(() => ({
+        href: 'https://debug.dhis2.org/dev/',
+        pathname: '/dev/',
+    }))
+
+afterEach(() => {
+    jest.clearAllMocks()
+})
+
+test('an absolute URL is used if provided as the default', () => {
+    const testBaseUrl = 'http://localhost:8080/hmis/long/path/dev'
+
+    const url = getBaseUrl(testBaseUrl)
+
+    expect(url).toBe(testBaseUrl)
+})
+
+describe('location variants', () => {
+    const defaultRelativeBaseUrl = '..'
+
+    for (const [testPath, expectedPath] of Object.entries(testPaths)) {
+        test(testPath, () => {
+            windowLocationMock.mockImplementation(() => ({
+                pathname: testPath,
+                href: testOrigin + testPath,
+            }))
+
+            const url = getBaseUrl(defaultRelativeBaseUrl)
+
+            expect(url).toBe(testOrigin + expectedPath)
+        })
+    }
+})
+
+test("if the function doesn't match a pattern, it falls back to the provided default", () => {
+    const relativeDefaultBaseUrl = '../../..'
+    const testPath = '/not/a/recognized/path/index.html'
+    windowLocationMock.mockImplementation(() => ({
+        pathname: testPath,
+        href: testOrigin + testPath,
+    }))
+
+    const url = getBaseUrl(relativeDefaultBaseUrl)
+
+    expect(url).toBe(testOrigin + '/not/')
+})