Beekeeping Hive Expansion Calculator

How the decision logic works

The calculator runs through six prioritized rules, returning the first one that matches your hive's state. The order is: split (swarm prevention) → super (production) → feed (winter prep) → treat varroa (timing-critical) → reduce entrance (defense) → wait.

The thresholds come from US beekeeping extension publications. The 7-of-10-frame rule for adding a super traces to UMaine extension; the 80% coverage + queen cells = split rule comes from NCSU; the post-harvest varroa treatment window timing comes from OSU.

The 7-frame rule and its exceptions

The conventional wisdom — add a super when bees cover 7 of 10 frames — is right most of the time during active flow in super season. But:

• If the flow has ended (you're in dearth), adding a super gives the bees more space to defend against robbing — usually a bad idea.
• If the queen has failed (no laying), the colony is shrinking, not growing — adding a super speeds the decline.
• If queen cells are present, the bees are already committed to swarming. Super first → still swarms. Split first → swarm avoided.

Splitting beats supering in some cases

For a strong hive in spring that's preparing to swarm, splitting produces two surviving colonies; supering produces one swarmed colony plus a feral swarm. The split is harder work but the outcome is far better. The calculator routes to split when queen cells are visible during split season.

Varroa treatment timing

Varroa pressure builds through the summer. By August in most zones, mite counts have reached the threshold where untreated colonies will collapse. The "treatment window" the calculator flags is the period when most natural beekeepers (Apivar, formic acid, oxalic acid) work effectively without honey supers on the hive.

When this calculator is the wrong tool

Use direct beekeeping mentorship or an extension agent for: queen rearing decisions, urban-suburban swarm legalities, commercial pollination scheduling, or diagnosis of European Foulbrood or American Foulbrood (both require lab confirmation and specific protocols not covered here).