<?xml version="1.0" encoding="us-ascii"?><InstanceReport xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"><Version>2.2.0.25</Version><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios><ReportLongName>2104100 - Disclosure - Share-based payments</ReportLongName><DisplayLabelColumn>true</DisplayLabelColumn><ShowElementNames>false</ShowElementNames><RoundingOption /><HasEmbeddedReports>false</HasEmbeddedReports><Columns><Column><Id>1</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><LabelColumn>false</LabelColumn><CurrencyCode>USD</CurrencyCode><FootnoteIndexer /><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios><MCU><KeyName>1/1/2011 - 3/31/2011
USD ($)

USD ($) / shares
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No documentation exists for this element. --</ElementDefenition><IsTotalLabel>false</IsTotalLabel><IsEPS>false</IsEPS><Label>Share Based Payments [Abstract]</Label></Row><Row><Id>3</Id><IsAbstractGroupTitle>false</IsAbstractGroupTitle><Level>0</Level><ElementName>us-gaap_DisclosureOfCompensationRelatedCostsShareBasedPaymentsTextBlock</ElementName><ElementPrefix>us-gaap</ElementPrefix><IsBaseElement>true</IsBaseElement><BalanceType>na</BalanceType><PeriodType>duration</PeriodType><ShortDefinition>No definition available.</ShortDefinition><IsReportTitle>false</IsReportTitle><IsSegmentTitle>false</IsSegmentTitle><IsSubReportEnd>false</IsSubReportEnd><IsCalendarTitle>false</IsCalendarTitle><IsTuple>false</IsTuple><IsEquityPrevioslyReportedAsRow>false</IsEquityPrevioslyReportedAsRow><IsEquityAdjustmentRow>false</IsEquityAdjustmentRow><IsBeginningBalance>false</IsBeginningBalance><IsEndingBalance>false</IsEndingBalance><IsReverseSign>false</IsReverseSign><PreferredLabelRole>terselabel</PreferredLabelRole><FootnoteIndexer /><Cells><Cell><Id>1</Id><IsNumeric>false</IsNumeric><IsRatio>false</IsRatio><DisplayZeroAsNone>false</DisplayZeroAsNone><NumericAmount>0</NumericAmount><RoundedNumericAmount>0</RoundedNumericAmount><NonNumbericText>&lt;div style="font-family:Times New Roman;font-size:10pt;"&gt;&lt;div style="line-height:120%;padding-left:24px;text-align:left;text-indent:-24px;font-size:10pt;"&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;&amp;#160;&lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;padding-left:24px;text-align:left;text-indent:-24px;font-size:10pt;"&gt;&lt;font style="font-family:Arial;font-size:10pt;font-weight:bold;"&gt;Note 4 &amp;#8211; Share-based payments&lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;text-align:left;font-size:10pt;"&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;Total compensation costs charged against income for the Company&amp;#8217;s share-based compensation arrangements was $9.6 and $18.1 for the quarter and six months ended March 31, 2011, respectively, and $6.8 and $15.0 for the quarter and six months ended March 31, 2010, respectively, and was recorded in &lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;selling, general and administrative expense&lt;/font&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt; (SG&amp;amp;A) expense. The total income tax benefit recognized in the Consolidated Statements of Earnings and Comprehensive Income (Condensed) for share-based compensation arrangements was $3.5 and $6.7 for the quarter and six months ended March 31, 2011, respectively, and $2.5 and $5.5 for the quarter and six months ended March 31, 2010, respectively.&lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;font-size:10pt;"&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;&amp;#160;&lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;text-align:left;font-size:10pt;"&gt;&lt;font style="font-family:Arial;font-size:10pt;text-decoration:underline;"&gt;Restricted Stock Equivalents (RSE)&lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;font-size:10pt;"&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;&amp;#160;&lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;text-align:left;font-size:10pt;"&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;In October 2010, the Company granted RSE awards to certain employees which included approximately 313,300 shares that vest ratably in most cases over four years or upon death, disability or change of control. At the same time, the Company granted two RSE awards to key executives. One grant includes approximately 86,700 shares and vests on the third anniversary of the date of grant or upon death, disability or change of control. The second grant includes approximately 202,300 shares which vests on the date that the Company publicly releases its earnings for its 2013 fiscal year contingent upon the Company&amp;#8217;s compound annual growth rate for reported earnings per share (EPS CAGR) for the three year period ending on September 30, 2013. Under the terms of the award, 100% of the grant vests if an EPS CAGR of at least 12% is achieved, with smaller percentages vesting if the Company achieves an EPS CAGR between 5% and 12%. In addition, the terms of the performance awards provide that the awards vest upon death, disability and in some instances upon change of control. The total performance award expected to vest will be amortized over the vesting period.&lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;font-size:10pt;"&gt;&lt;font style="font-family:inherit;font-size:10pt;"&gt;&amp;#160;&lt;/font&gt;&lt;/div&gt;&lt;div style="line-height:120%;text-align:left;font-size:10pt;"&gt;&lt;font style="font-family:Arial;font-size:10pt;"&gt;In November 2010, the Company granted two RSE awards to executive officers. One grant includes approximately 47,900 shares and vests on the third anniversary of the date of grant or upon death, disability or change of control. The second grant includes approximately 111,700 shares which vests on the date that the Company publicly releases its earnings for its 2013 fiscal year contingent upon the Company&amp;#8217;s EPS CAGR for the three year period ending on September 30, 2013. Under the terms of the award, 100% of the grant vests if an EPS CAGR of at least 12% is achieved, with smaller percentages vesting if the Company achieves an EPS CAGR between 5% and 12%. In addition, the terms of the performance awards provide that the awards vest upon death, disability and in some instances upon change of control. The total performance award expected to vest will be amortized over the vestin&lt;/font&gt;&lt;/div&gt;&lt;/div&gt;</NonNumbericText><NonNumericTextHeader>&amp;#160;Note 4 &amp;#8211; Share-based paymentsTotal compensation costs charged against income for the Company&amp;#8217;s share-based compensation arrangements was $9.6</NonNumericTextHeader><FootnoteIndexer /><CurrencyCode /><CurrencySymbol /><IsIndependantCurrency>false</IsIndependantCurrency><ShowCurrencySymbol>false</ShowCurrencySymbol><DisplayDateInUSFormat>false</DisplayDateInUSFormat><hasSegments>false</hasSegments><hasScenarios>false</hasScenarios></Cell></Cells><OriginalInstanceReportColumns /><Unit>Other</Unit><ElementDataType>us-types:textBlockItemType</ElementDataType><SimpleDataType>string</SimpleDataType><ElementDefenition>Disclosure of compensation-related costs for share-based compensation which may include disclosure of policies, compensation plan details, allocation of stock compensation, incentive distributions, share-based arrangements to obtain goods and services, deferred compensation arrangements, employee stock ownership plan details and employee stock purchase plan details.</ElementDefenition><ElementReferences>Reference 1: http://www.xbrl.org/2003/role/presentationRef
 -Publisher FASB
 -Name Statement of Financial Accounting Standard (FAS)
 -Number 123R
 -Paragraph 64, 65, A240

Reference 2: http://www.xbrl.org/2003/role/presentationRef
 -Publisher AICPA
 -Name Statement of Position (SOP)
 -Number 93-6
 -Paragraph 53

Reference 3: http://www.xbrl.org/2003/role/presentationRef
 -Publisher SEC
 -Name Staff Accounting Bulletin (SAB)
 -Number Topic 14

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