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Calculadora Capital

Savings Certificates Calculator

The Portuguese State’s capital-guaranteed savings product. Pick your series, F on sale or E closed in June 2023, and see what it earns after the 28% withholding tax.

Enter the base rate IGCP published for new Série F subscriptions that month (the 3-month Euribor average). The calculator adds Série E's extra percentage point and each year's permanence premium for you.

Net value at maturity
€12,315.24
Net interest
€2,315.24
Base rate of this series2.50%
Gross value (before tax)€13,350.19
Tax paid−€1,034.95

Year-by-year growth

YearGross rateGross valueNet value
12.50%€10,252.35€10,181.22
22.75%€10,537.21€10,384.31
32.75%€10,829.99€10,591.45
42.75%€11,130.90€10,802.72
52.75%€11,440.17€11,018.21
63.00%€11,787.26€11,258.14
73.00%€12,144.87€11,503.29
83.00%€12,513.34€11,753.78
93.00%€12,892.98€12,009.73
103.50%€13,350.19€12,315.24

Educational estimate, not financial advice. Assumes a constant base rate; the real value varies with the monthly rates.

Video: how to use the calculator

Two live series, on different rates

Certificates are issued in series and each has its own rules. Série F is the only one accepting new subscriptions, runs for 15 years and has a base rate capped at 2.5%. Série E stopped accepting subscriptions in June 2023, but the ones already made keep earning until each reaches its 10th anniversary, which means up to 2033. The difference that matters: Série E’s base rate is the same monthly rate plus 1 percentage point, with its own 3.5% cap. Anyone holding Série E earns considerably more today than someone subscribing to Série F.

How the interest rate is calculated

The return always has two parts: a base rate and a permanence premium added on top. The base rate is set every month and tracks the 3-month Euribor average (E3), rounded to three decimals. In Série F the base rate is E3 itself, capped at 2.5%; in Série E it is E3 plus 1 percentage point, capped at 3.5%. In September 2026 that gives 2.500% for Série F and 3.500% for Série E, which means both series now sit exactly at their legal ceiling: the base rate cannot rise any further, however far Euribor goes. The permanence premium is never subject to those caps, it is added afterwards.

The permanence premium of each series

In Série F the premium rises in five steps across the 15 years: +0.25% from year 2 to 5, +0.50% from year 6 to 9, +1.00% in years 10 and 11, +1.50% in years 12 and 13 and +1.75% in years 14 and 15. Série E has only two steps, but more generous ones early on: +0.50% from year 2 to 5 (double Série F) and +1.00% from year 6 to 10. Adding it all up, a Série E certificate subscribed in 2020 earns 4.500% gross today, while a Série F one in the same year 10 would earn 3.500%.

Quarterly compounding and the 28% tax

Interest is capitalised at the end of each quarter (annual rate ÷ 4), so the next quarter earns on a larger balance. As capital income, it is taxed at a flat 28% withholding rate at source; what compounds is the net interest. The calculator therefore highlights the net value (what you actually receive) and also shows the gross value for comparison.

Worked example

With €10,000 and the 2.500% base rate in force in September 2026, held for 10 years in Série F, you finish with about €12,315 net, roughly €2,315 of interest after tax. In year 10 the gross rate is 3.500% (the 2.500% base plus the 1% premium). The same €10,000 already held in Série E, on a 3.500% base rate, would finish those 10 years at about €13,515 net, which is €1,200 more than Série F. That is the difference you give up by redeeming Série E to subscribe again, and it cannot be undone, because Série E no longer accepts subscriptions.

Frequently asked questions

What is the savings-certificate interest rate today?
In September 2026 the Série F base rate is 2.500% (it was 2.474% in August). It is updated every month and tracks the 3-month Euribor, capped at 2.5%, and it has now reached exactly that legal maximum: it cannot rise further even if Euribor does. In Série E the base rate is that same rate plus 1 percentage point, with its own 3.5% ceiling, so it is likewise at the maximum, 3.500%. On top of either comes the permanence premium for the years held, which is not subject to the cap. Check the month’s figure on the IGCP website and enter it in the calculator.
I still hold Série E certificates: is it worth moving to Série F?
As a rule, no. Série E pays the same base rate plus 1 percentage point and has a higher permanence premium in the first five years, so it earns more than Série F under any comparable rate scenario. In this calculator, €10,000 in Série E over 10 years earns about €1,198 more net. And the decision is final: Série E closed to new subscriptions in June 2023, so anyone who redeems can only come back through Série F.
Is the interest taxed?
Yes, in both series. Interest is capital income and is taxed at 28% (the flat withholding rate) at source. What compounds is the net interest, so the calculator shows the net value as the main result.
What is the permanence premium?
It is an add-on to the base rate that rises the longer you hold the certificates. In Série F it starts at +0.25% in year 2 and reaches +1.75% in years 14 and 15; in Série E it is +0.50% from year 2 to 5 and +1.00% from year 6 to 10. It rewards long-term saving and is not subject to the base-rate cap.
Can I withdraw the money whenever I want?
You can redeem from the first interest date, that is after the third month. You get back the capital, which is always guaranteed, plus the interest capitalised up to that date. What you give up are the permanence premiums of the later years, which are the product’s biggest advantage.
Is there a maximum per person?
Yes. Each savings account can hold at most 250,000 Série F units (€250,000) and, counting Série F and Série E together, the combined ceiling is 500,000 units. The minimum subscription is 10 units. These ceilings can be changed by order of the government member responsible for Finance.

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Author: Thorben Rasmus Idel · Reviewed by: Nahar Geva · Last reviewed: 2026-09-01