How to make Flatlist faster

React Native's FlatList is the go-to for rendering large lists, but the defaults leave a lot of performance on the table. Lag, dropped frames, and unnecessary re-renders are almost always fixable with a handful of props and component patterns. Here's what actually moves the needle.

1. Always set keyExtractor

Without keyExtractor, React Native falls back to the array index as a key. Index keys break reconciliation when items reorder or get inserted. The virtual DOM diffing can't tell which items changed, so it re-renders everything.

// Bad — index as key (default)
<FlatList data={data} renderItem={renderItem} />

// Good — stable unique ID
<FlatList
  data={data}
  keyExtractor={(item) => item.id}
  renderItem={renderItem}
/>

Use a stable, unique field from your data: id, uuid, anything that won't change when the list updates.

2. Add getItemLayout when item height is fixed

By default, FlatList measures every item on mount to build its scroll offset map. If your rows have a fixed or predictable height, skip the measurements entirely with getItemLayout. This also unlocks scrollToIndex, which can't work without layout info.

const ITEM_HEIGHT = 72

<FlatList
  data={data}
  keyExtractor={(item) => item.id}
  getItemLayout={(_, index) => ({
    length: ITEM_HEIGHT,
    offset: ITEM_HEIGHT * index,
    index,
  })}
  renderItem={renderItem}
/>

For variable-height rows, skip this prop. An incorrect value will render items in the wrong positions.

3. Memoize renderItem with React.memo

Every time the parent re-renders, a new function reference is created for renderItem and FlatList re-renders all visible rows. Wrap the item component in React.memo and define renderItem outside the component or with useCallback.

// Item component — memoized
const ListItem = React.memo(({ item }: { item: Item }) => (
  <View style={styles.row}>
    <Text>{item.title}</Text>
  </View>
))

// In the parent — stable reference
const renderItem = useCallback(
  ({ item }: { item: Item }) => <ListItem item={item} />,
  [],
)

<FlatList data={data} keyExtractor={(item) => item.id} renderItem={renderItem} />

Without React.memo, the item still re-renders even if renderItem reference is stable, because React can't know the props didn't change.

4. Tune render batch sizes

Three props control how many items render at once. The defaults are conservative, reasonable for slow devices but usually worth increasing on modern hardware.

<FlatList
  data={data}
  keyExtractor={(item) => item.id}
  renderItem={renderItem}
  initialNumToRender={10}      // items rendered on first paint
  maxToRenderPerBatch={10}     // items rendered per JS frame during scroll
  windowSize={5}               // multiplier: viewable height × windowSize kept in memory
/>

initialNumToRender: Set it to exactly what fits on screen and nothing extra. Extra items delay first paint.

maxToRenderPerBatch: Higher = fewer blank flashes when scrolling fast, but heavier JS frames.

windowSize: Default is 21 (10 viewports above + 10 below). Reduce it to 5 to 7 to cut memory on long lists.

5. Enable removeClippedSubviews

On Android especially, off-screen views still sit in the native view hierarchy and eat GPU memory. removeClippedSubviews detaches their native views while keeping the JS component alive.

<FlatList
  data={data}
  keyExtractor={(item) => item.id}
  renderItem={renderItem}
  removeClippedSubviews={true}
/>

Caveat: can cause blank flashes during very fast scrolling on iOS. Test on device before shipping.

6. Never use inline styles or inline functions in renderItem

Inline objects and functions create new references on every render, defeating memoization.

// Bad — new object every render, breaks React.memo
<View style={{ padding: 16, flex: 1 }}>

// Good — stable reference
const styles = StyleSheet.create({
  row: { padding: 16, flex: 1 },
})
<View style={styles.row}>

Same rule applies to callbacks passed as props into the item: onPress={() => handlePress(item.id)} inside renderItem creates a new function per item per render. Bind the ID in the item component itself instead.

7. Use ListEmptyComponent, not a conditional wrapper

Wrapping FlatList in a conditional to show an empty state forces a full unmount/remount cycle when data arrives. Use the built-in prop. It renders inside the same scroll context and won't reset scroll position.

const Empty = () => (
  <View style={styles.empty}>
    <Text>No results found</Text>
  </View>
)

<FlatList
  data={data}
  keyExtractor={(item) => item.id}
  renderItem={renderItem}
  ListEmptyComponent={Empty}
/>

8. Paginate with onEndReached instead of loading all data up front

Loading 1000 items at once will choke the JS thread on first render. Fetch the first page, then append as the user approaches the end.

const [data, setData] = useState<Item[]>([])
const [page, setPage] = useState(1)
const [loading, setLoading] = useState(false)

const loadMore = useCallback(async () => {
  if (loading) return
  setLoading(true)
  const next = await fetchPage(page)
  setData((prev) => [...prev, ...next])
  setPage((p) => p + 1)
  setLoading(false)
}, [loading, page])

<FlatList
  data={data}
  keyExtractor={(item) => item.id}
  renderItem={renderItem}
  onEndReached={loadMore}
  onEndReachedThreshold={0.5}   // trigger when 50% from bottom
  ListFooterComponent={loading ? <ActivityIndicator /> : null}
/>

9. Avoid state updates inside renderItem

Any setState call triggered during a render pass will queue another render pass. If your item component needs local state (e.g., an expanded/collapsed toggle), keep it strictly local inside the memoized item component, and don't bubble it up to the list parent.

10. Use FlashList for very large datasets

If you've applied all of the above and scrolling is still janky on large lists, reach for Shopify's FlashList. It's a drop-in replacement that recycles native cell views (like RecyclerView on Android), cuts memory usage by ~50%, and maintains 60fps on lists where FlatList gives up.

import { FlashList } from '@shopify/flash-list'

// Same API as FlatList — swap the import
<FlashList
  data={data}
  keyExtractor={(item) => item.id}
  renderItem={renderItem}
  estimatedItemSize={72}   // required — helps FlashList pre-allocate cells
/>

FlashList requires estimatedItemSize instead of getItemLayout. Close is good enough, since it corrects on the fly.

The full optimized pattern

import React, { useCallback, useState } from 'react'
import { FlatList, StyleSheet, Text, View } from 'react-native'

const ITEM_HEIGHT = 72

const ListItem = React.memo(({ item }: { item: Item }) => (
  <View style={styles.row}>
    <Text style={styles.title}>{item.title}</Text>
  </View>
))

export function MyList({ initialData }: { initialData: Item[] }) {
  const [data, setData] = useState(initialData)
  const [page, setPage] = useState(2)
  const [loading, setLoading] = useState(false)

  const renderItem = useCallback(
    ({ item }: { item: Item }) => <ListItem item={item} />,
    [],
  )

  const loadMore = useCallback(async () => {
    if (loading) return
    setLoading(true)
    const next = await fetchPage(page)
    setData((prev) => [...prev, ...next])
    setPage((p) => p + 1)
    setLoading(false)
  }, [loading, page])

  return (
    <FlatList
      data={data}
      keyExtractor={(item) => item.id}
      renderItem={renderItem}
      getItemLayout={(_, index) => ({
        length: ITEM_HEIGHT,
        offset: ITEM_HEIGHT * index,
        index,
      })}
      initialNumToRender={12}
      maxToRenderPerBatch={10}
      windowSize={7}
      removeClippedSubviews
      onEndReached={loadMore}
      onEndReachedThreshold={0.5}
    />
  )
}

const styles = StyleSheet.create({
  row: { height: ITEM_HEIGHT, paddingHorizontal: 16, justifyContent: 'center' },
  title: { fontSize: 16 },
})

This covers the 90% case. Profile with Flipper or React DevTools before and after. The frame rate chart will tell you exactly which prop helped for your specific data shape.