# Maximum read lengths and number of cycles for different NextSeq 500/550 kits

**Maximum supported read length**

* Illumina platforms and sequencing kits allow for a variety of sequencing applications.
* To achieve the highest level of quality, Illumina supports reads up to a certain length depending on the sequencing platform and SBS kit version.
* It is possible to choose a longer read length during run setup in Local Run Manager (LRM) or the instrument control software.
  * When the read length exceeds the supported length Illumina cannot guarantee maintaining high data quality.

**Maximum read length for NextSeq 500/550 runs**

| SBS Kit Version | Maximum Read Length |
| --------------- | ------------------- |
| Mid-Output      | 2 x 151 bp          |
| High-Output     | 2 x 151 bp          |

**Maximum read lengths for index reads for NextSeq 500/550 runs**

* Instrument control software
  * Enter custom Index Read length during run setup as shown in the table below.
* LRM v2
  * Enter up to 100 characters maximum for the index cycles.\
    \- For further information, search for Knowledge Base article **Local Run Manager 2 - How to use a custom library prep kit**.
* For the highest sequencing quality of the Index Read, do not exceed the supported read length.

| <p><strong>NextSeq Control Software (NCS)</strong><br><strong>version</strong></p> | <p><strong>Single or Dual Index</strong><br><strong>(Maximum Length)</strong></p> |
| ---------------------------------------------------------------------------------- | --------------------------------------------------------------------------------- |
| NCS v2                                                                             | 20 bp                                                                             |
| NCS v4                                                                             | 20 bp                                                                             |

**Number of guaranteed cycles of SBS chemistry in each kit type for the NextSeq 500/550**

* Making sure 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, and can result in a run failure.
* Dual-index sequencing, depending on the instrument, follows different workflows as shown in the [Indexed Sequencing Overview Guide](https://emea.support.illumina.com/downloads/indexed-sequencing-overview-15057455.html).

The following table outlines available reagent kit sizes and the maximum number of cycles each kit can perform on the NextSeq 500/550.

| **Reagent Type** | **Reagent Kit Size** | <p><strong>Maximum Number</strong><br><strong>of Cycles</strong></p> | <p><strong>Additional Cycles Needed</strong><br><strong>for Dual Index?</strong></p> |
| ---------------- | -------------------- | -------------------------------------------------------------------- | ------------------------------------------------------------------------------------ |
| HO or MO         | 75                   | 92                                                                   | No                                                                                   |
| HO or MO         | 150                  | 168                                                                  | No                                                                                   |
| HO or MO         | 300                  | 318                                                                  | No                                                                                   |

HO = High-output, MO = Mid-output

For information regarding other Illumina sequencing platforms, search for Knowledge Base articles **Maximum read length for Illumina sequencing platforms** and **How many cycles of SBS chemistry are in my kit?**

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