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Free tool · HAM

HAM Price Index Multiple calculator

Index hybrid annuity payments with the 70:30 WPI and CPI(IW) Price Index Multiple, from the index values you type.

Free · Runs in your browser · No sign-up

Education only. The tool uses only the numbers you type. It is not investment, tax, legal or accounting advice and it does not recommend any security or transaction. The concession agreement decides the exact index months, rounding and which payments are indexed. This tool does not fetch index values: type the published WPI and CPI(IW) figures yourself.

Base and weights

30%

Payments to index

Index values and payments
Payment or dateWPI on its reference dateCPI(IW) on its reference dateAmount at bid pricesRemove

Everything runs in your browser. Nothing you type or open is uploaded, saved or sent. The sample index values are made up for illustration.

Latest Price Index Multiple
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Bid project cost at latest PIM
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Payments at bid prices
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Payments after indexation
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The formula

Price Index Multiple = 70% × (WPI now ÷ WPI at base) + 30% × (CPI(IW) now ÷ CPI(IW) at base), where the base is the reference index before the bid date. Under the hybrid annuity model the bid project cost is indexed this way until the commercial operation date, and the O&M payments are indexed too (CARE Ratings HAM methodology, October 2022).

Indexed amount = amount at bid prices × PIM. WPI is published by the Office of the Economic Adviser (DPIIT) and CPI(IW) by the Labour Bureau. If an index series is rebased, use the official linking factor so that both values are on the same base.

To see the full HAM payment profile, use the HAM annuity schedule (L), and read BOT, TOT and HAM.

Last reviewed 25 October 2026. Spotted an error? Tell us and we will correct it.