When you create a Planet Subscription with a start_time in the past, the Subscriptions API treats every scene that intersects your area of interest (AOI) between that start time and now as a backfill delivery. Backfill deliveries consume Area Under Management (AUM) and Processing Units (PUs) from your plan immediately, the same way forward-going deliveries do. A subscription opened with a start date several years ago can therefore exhaust a small or test plan in a single run.

This article explains how the API charges for backfill, what to check before you create a subscription, and what to do if a test subscription consumed more quota than expected.

How backfill consumption works

Each Planet Subscription has a start_time and an end_time. The API classifies the subscription based on those values:

• Backfill: both start_time and end_time are in the past.
• Forwardfill: end_time is in the future.
• Mixed: start_time is in the past and end_time is in the future. The API delivers a backfill segment for the historical window, then continues forwardfill for the remaining period.

For each backfill or mixed subscription, the API finds every Planet scene that intersects the AOI between start_time and the current time, then processes and delivers them according to the subscription's tools, source, and filters. AUM is charged based on the AOI area and the historical date range. PUs are charged for the processing performed on each delivered scene.

A 0.44 km AOI with start_time set to 2016-01-01 can consume well over 1,000 km of AUM and tens of thousands of PUs as the API works through ten years of PlanetScope archive. Cancelling the subscription stops further deliveries but does not refund AUM or PUs already consumed.

Check these values before you create a subscription

1. Review start_time and end_time. Confirm both values are the dates you actually want delivered. A test subscription that only needs to verify the API contract can use a start_time within the last day or two.
2. Estimate the backfill cost. Multiply your AOI area (in square kilometers) by the number of historical days between start_time and today. Compare the result against your remaining AUM. If the estimate exceeds your remaining quota, narrow the date range or the AOI before submitting.
3. Confirm your plan's AUM and PU balance. Use the Subscriptions API quota check or the Insights Platform account page to see what is available.
4. Test with a one-day window first. For new integrations, set start_time to yesterday and end_time to today. This verifies the API call without consuming a meaningful share of your plan.

What an update (PUT) does and does not change

You can update a running forwardfill subscription by sending a PUT to /subscriptions/{id}. The update applies to future item publications and deliveries only. The API does not redeliver items already produced and does not refund quota for past deliveries.

• Changing the AOI geometry on a pending subscription applies the new geometry to all deliveries in the subscription window, because no items have been published yet.
• Changing the AOI geometry on a running subscription applies the new geometry to items published from the moment of the PUT forward. Items already published with the previous geometry remain delivered with that geometry.
• start_time cannot be updated if it is in the past. Other immutability rules are listed in the Update a subscription section of the Subscriptions Mechanics page.

If a subscription consumed more quota than expected

1. Cancel the subscription if it is still running. Cancellation does not refund consumed AUM or PUs, but it prevents further consumption.
2. Open a support ticket with the subscription IDs, the AOI, the start_time and end_time values, and the consumed quota figures from your account page. Support cannot reverse plan consumption automatically, but the team can review whether a one-time courtesy adjustment applies, particularly for clearly test-shaped usage.
3. Ask your account team about enabling hard caps on the plan tier so the API rejects requests that would exceed prepaid quota, rather than processing them.

Related resources

• Planet Subscriptions API overview
• Planet Subscriptions API mechanics
• How does Area Under Management quota work?
• What are Processing Units (PUs) and how are they consumed?
• Subscriptions API FAQs