xslt-lab/site/content/xslt/functions/xpath-sum.md

title, description, date, version, versionLabel, category, syntax, tags

title	description	date	version	versionLabel	category	syntax	tags
sum()	Returns the sum of the numeric values in a node-set or sequence, or a specified zero value for empty sequences.	2026-04-18T00:00:00Z	1.0	XSLT 1.0	numeric function	sum(node-set)	xslt reference xslt1 xpath

Description

sum() converts each node in a node-set to a number (using the XPath number() rules) and returns their total as a double. If any node cannot be converted to a number, its value is treated as NaN, and the entire result is NaN.

In XSLT 2.0+, sum() accepts any sequence of atomic values that can be added together. A second argument may be provided as a zero value to return when the sequence is empty (in XPath 1.0, sum() on an empty node-set returns 0).

sum() is the standard way to compute totals over repeated elements, such as order amounts, quantities, or scores, without writing an explicit loop.

Parameters

Parameter	Type	Required	Description
node-set	node-set / sequence	Yes	The nodes or items to sum. Each is converted to a number.
zero	atomic value	No	Value to return if the sequence is empty (XPath 2.0+). Defaults to 0.

Return value

xs:double (XPath 1.0) or the type matching the input sequence (XPath 2.0+) — the numeric sum of all items.

Examples

Sum all child element values

Input XML:

<?xml version="1.0" encoding="UTF-8"?>
<invoice>
  <line amount="29.99"/>
  <line amount="14.50"/>
  <line amount="5.00"/>
</invoice>

Stylesheet:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output method="text"/>

  <xsl:template match="/invoice">
    <xsl:text>Total: </xsl:text>
    <xsl:value-of select="sum(line/@amount)"/>
  </xsl:template>
</xsl:stylesheet>

Output:

Total: 49.49

Conditional sum (sum filtered values)

Input XML:

<?xml version="1.0" encoding="UTF-8"?>
<sales>
  <sale region="North" amount="100"/>
  <sale region="South" amount="250"/>
  <sale region="North" amount="175"/>
  <sale region="South" amount="80"/>
</sales>

Stylesheet:

<?xml version="1.0" encoding="UTF-8"?>
<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
  <xsl:output method="xml" indent="yes"/>

  <xsl:template match="/sales">
    <totals>
      <north><xsl:value-of select="sum(sale[@region='North']/@amount)"/></north>
      <south><xsl:value-of select="sum(sale[@region='South']/@amount)"/></south>
    </totals>
  </xsl:template>
</xsl:stylesheet>

Output:

<totals>
  <north>275</north>
  <south>330</south>
</totals>

Empty sequence with fallback (XSLT 2.0)

<!-- Returns 0 when there are no discount elements -->
<xsl:value-of select="sum(discount/@value, 0)"/>

Notes

• Nodes that cannot be converted to a number (e.g., text like "N/A") produce NaN, which propagates through the sum. Validate data or use number() with a fallback before summing.
• sum() on an empty node-set returns 0 in XPath 1.0. In XPath 2.0+, the second argument controls this behaviour.
• For an average, there is no built-in avg() in XPath 1.0. Compute it as sum(nodes) div count(nodes). XPath 2.0+ provides avg().
• sum() works on attribute nodes as well as element text nodes; the path sum(items/item/@qty) is valid.

See also

• count()