Calculate price adjustment with the official formula
Enter the coefficients from your contract and let the indices load from TÜİK data. The calculation follows the formula in the Turkish Principles for Price Adjustment in Works Contracts. No sign-up.
Your progress payment's price adjustment
Enter the coefficients exactly as the contracting authority's INDEX sheet lists them. Values of the series published on this site and EPDK fuel prices fill in by themselves.
How price adjustment is calculated
In Turkish public works, price adjustment follows the formula in the Principles for Price Adjustment in Works Contracts. The calculator applies it as written.
F = An × B × (Pn − 1)
Pn = a(İn/İo) + b1(Çn/Ço) + b2(Dn/Do) + b3(AYn/AYo) + b4(Yn/Yo) + b5(Kn/Ko) + b6(Gn/Go) + c(Mn/Mo)
An is the value of the work done in the application month at contract prices. B is 0.90. Each term of Pn multiplies an input's weight by the ratio of its current to its base index.
| Coefficient | Input | Index |
|---|---|---|
| a | Labour | CPI General (2003=100, linked series from 2026), single index |
| b1 | Other non-metallic mineral products | Domestic PPI 23 and its groups |
| b2 | Iron and steel products | Domestic PPI 24 and its groups |
| b3 | Motor fuel | EPDK sales price, from the bulletin |
| b4 | Other solid or liquid fuels | Domestic PPI 19 and its groups |
| b5 | Wood and cork products | Domestic PPI 16 and its groups |
| b6 | Other materials | Domestic PPI series set by the authority; General if none |
| c | Depreciation of machinery and equipment | Domestic PPI 28 and its groups |
Rules of the calculation
- Base index (Io)
- The index of the month the tender date falls in. For fuel, the sales price on the tender day. (art. 4/1-ı)
- Current index (In)
- The index of the application month; for fuel, that month's average sales price. The application month is when the work was due under the work schedule. (art. 4/1-ç, 4/1-i)
- B = 0.90
- The fixed coefficient of the formula; it does not vary by contract. (art. 5/2-c)
- Coefficients add up to 1.00
- The authority sets the coefficients in the tender documents so that they add up to one; they cannot change during the contract. (art. 5/3, 5/6)
- Advance deduction
- Where an advance was paid, the advance deducted in the payment comes off An before the calculation. Not when Pn is below one. (art. 6/6)
- When Pn is below 1
- The price adjustment is negative and is deducted from the payment. The Principles define it as an amount to be paid or deducted. (art. 4/1-e)
- When an index is not yet published
- The price adjustment is not calculated with the payment; it is calculated separately once the application month's indices are known. (art. 6/2)
What this tool does not calculate
It does not cover the lower-index rule for work behind schedule (art. 7/2), work carried on with penalties after the completion date, the provisional calculation with the previous month's indices when several payments fall in one month, the separate calculation of lump-sum and unit-price parts in mixed contracts, materials on site, or contracts under the 2013 Principles.
Indices are published by TÜİK and taken from the TCMB EVDS. Since January 2026 TÜİK has published the CPI on a 2025=100 base. The 2026 figures in the site's CPI General (2003=100) series are the 2025=100 series linked to the 2003=100 base (TCMB EVDS). The In/Io ratio comes out the same on both bases, apart from a very small rounding difference. The calculation is for information only.
About price adjustment
- Price IndicesDomestic PPI sub-indices and CPI, monthly tables since 2012.
- Progress Payment Deductions CalculatorThe cover's VAT, every deduction from a) to k) and the net amount paid to the contractor, on one sheet.
- Quantity Takeoff CalculatorRebar, concrete, formwork and excavation takeoffs: a measurement sheet with deductions, exact totals and a copy for Excel.
- Index Change CalculatorHow Domestic PPI and CPI moved since your tender month, with the In/Io ratio.
- Work Experience Update CalculatorWhat a work experience certificate counts for in the tender you enter, with the right Domestic PPI months for its kind.
- Stamp Duty CalculatorThe 9.48 per mille stamp duty on a progress payment, with the yearly cap.
- VAT Withholding CalculatorThe VAT withheld on a progress payment, at the communiqué's rate for the work type.
- Withholding Tax CalculatorWithholding tax on a multi-year construction payment, at the rate for the work type and payment month.
- Performance Bond CalculatorThe performance bond on a bid, with the below-limit 9% rule and additional bonds.
- Minimum Labour CalculatorThe minimum labour to declare for the SGK clearance, the shortfall and its estimated premium.
- Advance Payment CalculatorThe advance, its 30% or one-third cap, the recovery rate and what comes off each progress payment.
- Work Increase CalculatorThe work increase room left under the 20% (unit price) or 10% (lump sum) limit.
- Completion Compensation Calculator5% of the shortfall when work ends below 80%, updated to the acceptance month by Domestic PPI.
- Delay Penalty CalculatorThe delay penalty from the first contract price, daily rate and days late, with the 15% cap.
- Work Duration CalculatorCompletion date from the site handover, days late, final acceptance and payment deadlines.
- Fuel PricesEPDK monthly averages by fuel type, for the fuel coefficient of a price adjustment.
Stop doing this by hand on every payment
Enter the coefficients once; indices arrive every month and the price adjustment lands on the payment by itself.