Tax on savings interest

When you set up a savings portfolio, the app asks for a tax rate. This guide explains what that field is for, where to find your own number, and what happens if you get it wrong.

Educational content, not tax advice. Rates below are indicative headline figures for ordinary bank interest, last reviewed in August 2026. They ignore allowances, brackets and reliefs, they change, and they may not apply to your situation. Check with your bank or tax authority, or a qualified adviser.

What the field actually does

The tax rate tells the app how much of your interest you don't get to keep. It affects projections only — what the app expects your savings to be worth in future, and what it shows in the income calendar. It never changes the entries you record yourself, and it is not used for filing anything.

If the rate is too low, every projection is optimistic. That is the failure worth avoiding: a savings account projected at 5% when you actually keep 4.5% looks fine for a year and drifts badly over ten.

Where to find your rate

In rough order of how quickly it will answer the question:

1. Your bank statement. In many countries the bank deducts the tax before it pays you. If your statement shows "interest" and "tax withheld" as separate lines, the rate is the second divided by the first.
2. Your bank's savings account terms. Usually stated as a withholding or retention rate.
3. Your tax authority's website. Search for "tax on savings interest" plus your country.
4. Last year's tax return, if interest income appeared on it.

If your bank already deducts the tax and your statement only shows the amount that landed in your account, you can also just enter the interest you actually received and leave the tax rate at 0 — the projection then works from the net figure.

Common rates

The app prefills this field based on where your account says you are, and names the country so you can tell whether the guess was right. If it guessed wrong, change it — the number is a starting point, not an answer.

Countries with no single rate

For four places the app deliberately prefills nothing, because one number would mislead most readers:

• United Kingdom — a Personal Savings Allowance means many people pay 0% on savings interest up to a threshold. Above it, interest is taxed at your income-tax band. If your interest is within the allowance, use 0.
• United States — interest is ordinary income, taxed at your marginal federal rate, plus state tax where it applies. Use your marginal rate rather than a headline figure.
• Netherlands — the Box 3 system taxes an assumed return on your assets rather than the interest you actually received, so a per-interest rate doesn't map cleanly. Many people leave this at 0 and treat the tax separately.
• Switzerland — 35% is withheld at source, but you normally reclaim it when you declare the income. If you reclaim it, your effective rate is your ordinary income-tax rate, not 35%.

Changing it later

Nothing here is permanent. Open the portfolio, then Actions → Income settings, and change the tax rate whenever you learn the real figure. Existing entries you recorded yourself are untouched; only the projections are recalculated.

If you'd rather not think about it now, leave the prefilled value and come back — an approximately right rate is much better than 0, and far better than not creating the portfolio at all.