TL;DRPricing a window by walking whole units of the quoted price basis and scaling only the partial one.
Quoted ₹1,000 a month and invoiced quarterly from 1 January, but activated on 15 January? The window is priced as 17/31 of January plus a full February plus a full March — not ₹3,000 × 75/90.
The same rule runs in both directions. Splitting an amount already charged, for a credit or a downgrade, walks the same units, so a clean third is exact and March of that quarter credits exactly ₹1,000.
Full aligned cycles stay nominal; the walk only applies to stubs and sub-windows. Usage is never prorated — it is measured.
Where it happens in Sonic
Next
See it on your contracts
A walkthrough on the agreements and files you actually bill from — not a slide deck.