What is Lock Window?

The lock window is a mechanism in SKAdNetwork 4.0 that allows advertisers to end a measurement period early. When triggered, it freezes the current conversion value and tells Apple to prepare the corresponding postback.

Instead of waiting for a full 2-day, 7-day, or 35-day window to expire, you can lock it as soon as you believe the user has shown all relevant behavior, for example, completing onboarding and starting a trial within the first 24 hours.

How does it work?

SKAN 4.0 divides the measurement period into three fixed postback windows:

1. Day 0–2

2. Day 3–7

3. Day 8–35

If a user performs high-value actions early (like starting a subscription on Day 1), you can lock the first window to signal that the behavior is complete. This tells Apple to finalize the postback sooner, while still applying a randomized delay.

Locking is optional and must be set by your app logic or SDK. Once a window is locked, Apple stops accepting conversion value updates for that period.

Why it matters

The lock window gives advertisers more control over the timing and quality of postbacks. It allows:

• Faster feedback loops for campaign optimizationx

• Cleaner signals by avoiding noise from later, less-relevant user behavior

• Better alignment between your measurement strategy and actual user flow

For example, a fintech app might lock the first window as soon as a user links a bank account, since that’s the strongest early signal of long-term value. This lets the growth team access performance insights within days, not weeks.