When your savings account becomes a job.

Once your interest income clears a certain threshold, it stops being passive and starts being a thing you have to manage: tax, currency, rate-shopping, and the question of when a low rate is costing you more than the convenience is worth. A practical frame.

At a cash pile of roughly 500,000 NOK at 4-5% interest, the gap between a good savings account and a default one stops being a rounding error and becomes about a month of net pay every year. That income is taxable, responds to which account you keep it in, and costs you when you don’t pay attention. Here is the frame for when interest income becomes a job, and what to do about it once it does.

The threshold that catches people off guard

Quick math: a 500,000 NOK pile at 4.5% earns ~22,500 NOK a year, roughly one decent month of net pay. At 5% it’s closer to 25,000. That’s no longer ignorable. It’s also no longer passive. It is income that triggers tax, that responds to which account you keep it in, and that costs you when you don’t pay attention.

The dynamic is sneaky because the threshold moves with interest rates, not with you. In a 1% world a 500k pile earns nothing worth thinking about. In a 5% world that same 500k earns enough to fund a small holiday, every year, forever, with you doing nothing. The rate environment changed the math, your situation didn’t.

Tax: the part most people forget

Interest is taxable as income in most countries, and the tax rate varies enough to matter for where you keep your money. A short, non-exhaustive map:

• Norway. Capital income is taxed at ~22%. A 25,000 NOK gross interest year becomes ~19,500 NOK in your pocket. Worth knowing if you’re planning a purchase against expected interest income.
• UK. Personal Savings Allowance covers the first £1,000 of interest for basic-rate taxpayers (£500 for higher rate). Above that, it’s taxed as income at your marginal rate. ISAs sit outside this entirely.
• Germany. Capital gains and interest taxed at ~26% (Abgeltungsteuer) above the €1,000/€2,000 Sparer-Pauschbetrag annual allowance.

Three different countries, three different rules, three different optimal account strategies. People who treat interest as “just savings” ignore all of it.

The “rate threshold” decision

Once interest matters, every account on the list earns a question: is the rate good enough to leave money here? At 4.5% available elsewhere, a 0.5% legacy account is leaking 4% × balance × year, the cost of inertia priced honestly.

Worth doing the explicit math: pick a rate threshold below which an account is flagged. Anything paying less than (say) 3% gets a yellow tag and shows up in a “move this” queue. The threshold is personal: it depends on how much switching cost you tolerate, how much you value the convenience of the slower account, what the best available rate is.

The currency layer

A 5% rate in TRY is not better than a 3% rate in EUR if the lira loses 8% of its value during the year. Currency-of-account matters as much as rate. For most savers the right rule is simple: hold interest-bearing accounts in the currency you’ll spend the interest in. Exotic-currency yield chasing has buried better savers than us.

How fjordFIRE handles this

fjordFIRE’s Interest tracker rolls up every interest-earning account: balance, rate, monthly and annual income, currency. You set a rate threshold; accounts paying below it get flagged. A per-account What-If sandbox lets you ask “if I moved this 500k from 0.4% to 4.2%, what does that do to annual income?” Answered in seconds, in your currency. Tax is applied at the rate you set; the after-tax line is what you actually take home.

The annual projection rolls up across currencies. If you hold interest accounts in EUR, NOK, and USD, you see one consolidated annual interest income, and the per-currency table underneath shows where it’s coming from.

Go deeper: Net worth is one number (four-pillar) · Your savings rate is half FX.

Companion tools: Currency Conversion Cost calculator.