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Spanish Treasury Bill Calculator

Work out the real yield on a Spanish Letra del Tesoro from the price you paid, or the price implied by an auction yield, using the Tesoro’s own method, plus the gain after tax.

A letra has a nominal of €1,000 and the minimum purchase is €1,000. You buy below the nominal: that difference is the entire return, because a letra pays no coupons.

Annual yield
2.901 %
Gain (nominal − price)
€28.50

How the result is reached

Simple interest, 360-day year (term of 376 days or less)

Purchase price€971.50
Gain (nominal − price)€28.50
Annual yield2.901 %

After tax

Income tax on the gain€5.42
Effective rate19.00 %
Net gain€23.09

Letras del Tesoro carry NO withholding: nothing is retained at maturity and the whole gain is settled in your annual return. Worth planning for.

Educational estimate, not investment advice. Each auction yield is published by the Tesoro Público and differs with every issue. The savings brackets used are those in force for 2026: confirm them for later years.

Video: how to use the calculator

1

A letra pays no interest: it pays a discount

Letras del Tesoro are short-term securities issued at a discount. There are no coupons: you buy below the €1,000 nominal and are repaid the full €1,000 at maturity. That difference is the entire return, which is why price and yield are the same information seen two ways, and why a lower price means a higher yield.

2

The detail that breaks home-made spreadsheets: the year is 360 days

Article 14.1 of Orden ECM/2/2026 prints two formulas. Up to one natural year, simple interest on a 360-day year. Beyond one natural year, compound interest, and its exponent runs on 360 as well. Since letras are issued at 3, 6, 9 and 12 months, almost everything a retail buyer holds falls in the simple branch, but a 12-month letra can mature a few days past the year and switch formula: in the 2026 calendar the September and December lines do exactly that, running 371 days. This calculator always names the one it used.

3

No withholding, which changes the planning

Unlike a deposit, letras carry no withholding at source: at maturity the full nominal is paid and nothing is retained. The gain is still taxed as savings income, but the whole amount is settled in the following year’s return. It is worth setting that money aside rather than meeting it in June.

4

The gain stacks on your other savings income

The savings base is progressive and single: deposit interest, dividends and a letra’s gain accumulate together. If you already have savings income this year, the letra’s gain does not start again in the first bracket, it stacks on top. That is why the calculator asks: without it, any net estimate comes out optimistic.

Worked example

Example: a 12-month letra with a €1,000 nominal, bought at €971.50 with 364 days to maturity. The gain is €28.50, and because 364 days does not exceed one natural year it is annualised with simple interest on a 360-day year: 28.50 ÷ 971.50 × 360 ÷ 364 = 2.901% a year. With no other savings income, tax on that gain is €5.42 at 19%, leaving €23.09 net. In the other direction, an auction clearing at 3% over 364 days implies a price of €970.56.

Frequently asked questions

How is the yield on a letra calculated?
Divide the gain (nominal minus price) by the price paid and annualise. Up to one natural year the Tesoro uses simple interest on a 360-day year; beyond one natural year, compound interest with the exponent also on 360. Both formulas are printed in article 14.1 of Orden ECM/2/2026. This calculator applies the right method automatically and tells you which.
What is the minimum investment?
The minimum bid is €1,000, which is also a letra’s nominal, in multiples of €1,000 thereafter. You can bid at auction directly with the Tesoro, through your bank, or via a direct account at the Banco de España.
Do letras have tax withheld?
No, with one exception almost nobody mentions. Article 75.3.b) of the income tax regulation puts the return on letras outside withholding, so the full nominal is paid at maturity. Its second paragraph puts it back if you hold them through a bank account based on operations in letras, where the bank does withhold. Either way the gain is taxed in the savings base and settled in full in the following year’s return.
What if I sell before maturity?
You can sell on the secondary market at whatever price prevails, which depends on how rates have moved. If rates have risen since you bought, the price will have fallen and you can lose money; the guaranteed outcome only applies if you hold to maturity.
Why does my figure differ from the Tesoro’s?
For three reasons, in this order. First the day-count basis: the Tesoro annualises on 360 days, not 365. Second, the days run from the ISSUE date, three business days after the auction, not from auction day. And third, the average rate is published rounded down to three decimals while the amount actually charged uses every decimal, as point 3 of each results resolution states.

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Author: Thorben Rasmus Idel · Reviewed by: Nahar Geva · Last reviewed: