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Treasury Bill Calculator for Sri Lanka - Price, Yield and Return

Enter the amount you want to invest, the yield and the days to maturity to see what a Sri Lankan Treasury bill returns in rupees. Or turn a yield into a price, or a price back into a yield.

Maintained by Hirantha Sandaruwan Lakshan. Rules checked 13 October 2026 against Central Bank of Sri Lanka: Government Securities Market and 6 more sources.

About this tool

This tool has no market rates in it: Treasury bill rates change at every auction, so you enter the current one. It runs in your browser and sends nothing.

How it works

A Treasury bill pays no interest. The Central Bank of Sri Lanka (CBSL) sells it at a discount and repays the face value on maturity, so your return is the difference. CBSL auctions bills of 91, 182 and 364 days. In the auction notices, such as the one for 19 August 2026, the minimum bid is Rs. 5 million (then multiples of Rs. 1 million) and bids go through primary dealers, so most small investors buy through a primary dealer or a licensed bank, which can also sell bills with fewer days left.

The yield is a simple yearly rate on the price you pay. The price per Rs. 100 is 100 / (1 + yield x days / 364), and the yield is (100 / price - 1) x 364 / days. Many guides use a 365-day year. On 13 October 2026 we checked the Public Debt Management Office's (PDMO) published daily quotes: every maturity row of their table works out to a whole number of days on a 364-day year (1 month is 30 days, 3 months 91, 6 months 182 and 12 months 364) and to fractions of a day on a 365-day year, and a primary dealer's Treasury bill page lists an interest basis of 364 days. CBSL's own pages do not print the formula, so a switch lets you use 365 days if your dealer does.

The price is shown to 4 decimals per Rs. 100 and money to the cent. A dealer may round the price before multiplying, so a contract note can differ by a few rupees on a large amount. Fees and the dealer's margin are not included, and the figures assume you hold the bill to maturity.

On tax (checked on 13 October 2026), CBSL says government securities are not subject to withholding tax, and Inland Revenue Department circular SEC/2026/E/04 of 8 June 2026 says withholding tax is not required on interest or discount on Treasury bills. That is not an exemption from income tax: the Department's notice PN/IT/2024-03 of 11 December 2024 says the discount must be included in your assessable income, with no tax credit. The only exemptions it lists are for people outside Sri Lanka who bought with funds remitted to Sri Lanka and for Samurdhi community-based banks. Check your own position with your bank or the Department.

Worked examples

Rs. 1,000,000 for 91 days at an example 10% yield

The price is Rs. 97.5610 per Rs. 100. You receive Rs. 1,025,000.00 on maturity for the Rs. 1,000,000.00 you paid, a return of Rs. 25,000.00, which is 2.5% over the 91 days. The 10% is only an example.

Price from yield: Rs. 1,000,000 face value, 182 days, 10% yield

The price is Rs. 95.2381 per Rs. 100, so the bill costs Rs. 952,380.95 and returns Rs. 47,619.05 on maturity.

Yield from price: Rs. 97.5 per Rs. 100, 91 days

The yield is 10.256% a year. The return over the 91 days is 2.5641% of the price, and 2.5641% x 364 / 91 = 10.256%.

A 364-day bill at 10%

The price is Rs. 90.9091 per Rs. 100. A Rs. 1,000,000 face value costs Rs. 909,090.91 and returns Rs. 90,909.09. On a 364-day basis a 364-day bill is exactly one year.

Price per Rs. 100 at an example yield of 10%, on the two day bases

BillDaysPrice on a 364-day basisPrice on a 365-day basis
91-day9197.561097.5675
182-day18295.238195.2505
364-day36490.909190.9317

Frequently asked questions

What formula does a Sri Lankan Treasury bill use?

Price per Rs. 100 = 100 / (1 + yield x days / 364), and the yield is (100 / price - 1) x 364 / days. It is a simple yearly yield on the price paid. CBSL does not print the formula on the pages we checked, so this is the form that matches the Public Debt Management Office's published quotes.

Should I use 364 or 365 days?

Use 364 unless your dealer tells you otherwise. The Public Debt Management Office's daily quotes fit 364 exactly, and a primary dealer's page lists a 364-day interest basis. The difference is small: for a 91-day bill at 10% the price moves from 97.5610 to 97.5675 per Rs. 100.

Where do I find the current Treasury bill rate?

CBSL publishes the result of each auction as a weighted average yield for the 91, 182 and 364 day bills. The Public Debt Management Office publishes a daily report of secondary market quotes, and primary dealers and banks publish their own bid and offer rates. This tool does not fetch any rate, so type the one you have.

Is tax deducted from Treasury bill returns?

Not at source. CBSL says government securities are not subject to withholding tax. But the Inland Revenue Department says the discount is taxable income that you must include in your assessable income, with no tax credit, apart from two narrow exemptions (people outside Sri Lanka who bought with funds remitted to Sri Lanka, and Samurdhi community-based banks), so you may still owe income tax. This was checked on 13 October 2026. Ask your bank or the Department if you are unsure.

How is a Treasury bill different from a fixed deposit?

A Treasury bill is a government security sold at a discount and repaid at face value, with no interest payments, and it can be sold in the secondary market before it matures. A fixed deposit is a deposit with a bank that pays interest on a schedule. Use the fixed deposit calculator to compare them by yield.

Can I buy a bill with fewer than 91 days left?

Yes, in the secondary market from a primary dealer or a licensed bank, which is how CBSL says investors can buy outside the auction. Enter the days left, from 1 to 364. The dealer or bank sets its own terms and price.

Sources & references

Updated Oct 13, 2026