# How many cycles of SBS chemistry are in my kit?
Ensuring that sufficient volumes of SBS reagents are loaded onto the sequencing instrument is crucial for a successful run. Running out of reagents during a run impacts intensity and quality metrics, and can result in total run failure.
Dual-index sequencing follows different workflows depending on the instrument, as shown in the [Indexed Sequencing Overview Guide](https://emea.support.illumina.com/downloads/indexed-sequencing-overview-15057455.html). On certain instruments, dual-index runs require an additional seven cycles of reagents for the chemistry-only cycles at the beginning of the second Index Read. The seven chemistry-only cycles are required for the workflows in which the second Index Read sequencing occurs after the forward template anneals to the grafted P5 primer on the surface of the flow cell. These seven cycles must be considered when calculating the number of cycles supported by the kit.
The following table outlines available reagent kit sizes and the maximum number of cycles each kit can perform, taking the additional seven cycles into consideration when necessary:
\*The NextSeq 1000/2000 P2 v3 300 cycle kit has 338 total cycles while the P3 v3 300 cycle kit has 327 total cycles.
\*\*All the NextSeq 1000/2000 XLEAP kits have 38 extra cycles.
For details on maximum supported cycles in each read, refer to the article [Maximum read length for Illumina sequencing platforms](https://emea.support.illumina.com/bulletins/2020/04/maximum-read-length-for-illumina-sequencing-platforms.html).
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