Proration is where correctness and trust get tested. Decide your policy, then encode it as tests.
Common gotchas
- Time zones: store in UTC, render in customer timezone.
- Rounding: per line vs per invoice total (pick one and stick to it).
- Minimum charge thresholds.
- Trial → paid transitions and credits.
Treat proration behavior like an API contract—if it changes unexpectedly, finance will notice.
Neruba treats proration rules as explicit policy so behavior stays consistent across upgrades and downgrades.
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