Both dates are common search questions because they sit either side of a change. Here is how each lands, using the verified factor schedule.
The schedule by install date
| Install window | Factor | Tiers |
|---|---|---|
| 1 Jul to 31 Dec 2025 | 9.3 | None |
| 1 Jan to 30 Apr 2026 | 8.4 | None |
| 1 May to 31 Dec 2026 | 6.8 | 100% to 14 kWh, 60% to 28 kWh, 15% to 50 kWh |
| 1 Jan to 30 Jun 2027 | 5.7 | Tiers assumed to continue |
| 1 Jul to 31 Dec 2027 | 5.2 | Tiers assumed to continue |
A battery installed on 30 April 2026
The last day of the older rules. Factor 8.4, and the whole usable capacity up to 50 kWh counts at the full factor.
- 13.5 kWh: 13.5 x 8.4 = 113.4, so 113 STCs (about $4,300 to $4,520 at $38 to $40)
- 28 kWh: 28 x 8.4 = 235.2, so 235 STCs (about $8,930 to $9,400)
One day later, on 1 May, the same 28 kWh battery earns 152 STCs. That is a difference of 83 certificates, or roughly $3,000. For installers, the practical lesson is that the date on the paperwork must be right and supportable. A job that was physically finished on 30 April has to have photos and a record that show it.
A battery installed in December 2026
Any installation completed between 1 and 31 December 2026 is at 6.8 with tiers.
- 13.5 kWh: 13.5 x 6.8 = 91.8, so 91 STCs (about $3,458 to $3,640)
- 28 kWh: 14 x 6.8 + 14 x 6.8 x 0.6 = 152.32, so 152 STCs (about $5,776 to $6,080)
The pressure here is the calendar. Installing on 31 December means 91 certificates on a 13.5 kWh battery. Installing on 2 January means about 76. That gap is around $570 per job at current prices, which is why installers are scheduling carefully into late December. If the work slides, the customer or the installer carries the difference, so agree who does before the date arrives.
What this means for installers
- Treat the installation date as the pricing date and record it carefully. See which date counts for the installation versus commissioning point.
- Stock, grid approvals and weather are the usual reasons a December job slips. Build in a buffer, and tell customers in writing what happens if the job passes 31 December.
- Lodge complete claims promptly. The rate on our pricing page is locked when a complete claim is lodged, and 24-hour settlement for established partners keeps cash flow tight around a changeover. New to us? Start trading and the first claim clears in 48 to 72 hours.
What this means for homeowners
If you are choosing between installing before the new year or after, you are weighing a known certificate drop against the cost of rushing. A rebate difference of several hundred dollars is real, but a rushed installation or a poor battery choice costs more. Use the battery STC calculator to compare dates and see the battery STC pillar page for the full program. The insight on the 1 January 2027 changes goes deeper for installers.