The factor is the multiplier applied to usable kilowatt-hours. For 2026 it was 8.4 for the first four months and 6.8 from 1 May.
The 2026 numbers
| Commissioning period | Factor |
|---|---|
| July to December 2025 | 9.3 |
| January to April 2026 | 8.4 |
| May to December 2026 (current at the time of writing) | 6.8 |
A battery commissioned from 1 May to 31 December 2026 uses 6.8. The next steps are 5.7 on 1 January 2027 and 5.2 on 1 July 2027. See the 2027 factor and the full schedule in the 2028 to 2030 factors.
How much it fell on 1 May 2026
Two things changed on the same date: the factor fell from 8.4 to 6.8, and the tiers started. Together they hit larger batteries hardest.
| Usable kWh | STCs before (8.4, no tiers) | STCs after (6.8, tiered) | Change |
|---|---|---|---|
| 5 | 42 | 34 | -19% |
| 10 | 84 | 68 | -19% |
| 14 | 117 | 95 | -19% |
| 28 | 235 | 152 | -35% |
| 50 | 420 | 174 | -59% |
Up to 14 kWh the cut was the factor alone, about 19%, or roughly $850 on a 14 kWh battery at $38 to $40 per STC. For 28 kWh the cut was about 83 STCs, about $3,150 to $3,300. At 50 kWh it was about 246 STCs, about $9,300 to $9,800. See the tiers and the official summary of the changes.
What the factor means in dollars
Multiply the STC count by the certificate price. The market has been roughly $38 to $40 at the time of writing, with the clearing house ceiling at $40. A 10 kWh battery at 6.8 earns 68 STCs, so $2,600 to $2,700. Your installer sets the discount in your quote, and it should be consistent with this arithmetic.
What this means for installers
Re-check old quotes that straddle a factor date. Where the customer was quoted on 8.4 and the job commissions on 6.8, the shortfall is yours unless the quote said otherwise. Put a validity date on every battery quote and tie it to the commissioning date. Settlement of battery STCs is covered at /pricing/ and /start-trading/.
What this means for you
If you are choosing a date, the 2026 factor holds until 31 December. After that it falls to 5.7, then 5.2. Estimate your own with the battery STC calculator, and see the battery STCs pillar and the Cheaper Home Batteries installer guide.