How is savings account interest calculated?

Most NZ savings accounts calculate interest daily on your balance and pay it monthly. The annual rate is divided across the days, so a higher balance and a higher rate both earn more. Bonus-rate accounts pay extra if you meet conditions like no withdrawals.

Is savings interest taxed?

Yes. Resident Withholding Tax (RWT) is deducted at your chosen rate (matching your income tax rate). This calculator shows interest before and after RWT so you see what actually lands in your account.

How do regular deposits help?

Adding money regularly grows the balance that earns interest, so your interest compounds over time. Even small, consistent deposits make a meaningful difference over a year or more.

Savings Account Interest Calculator

This New Zealand calculator works out the interest you earn on an on-call savings account, before and after Resident Withholding Tax. It also shows how regular deposits grow the balance and the interest over a year. You enter your starting balance, the rate, your RWT rate and any monthly deposit, and the tool shows the interest earned and your end balance after tax.

Starting balance

Interest rate p.a.

Monthly deposit

Your RWT rate

interest earned in a year, after RWT

Interest before tax$0

RWT deducted$0

End balance$0

Assumes interest compounds monthly with your monthly deposit added. Bonus-rate accounts may pay more if you meet conditions. RWT is deducted at your chosen rate. Estimate only.

How it works

The calculator compounds your balance monthly at the annual rate, adding your monthly deposit each month, over a year. It totals the interest earned, deducts RWT at your chosen rate, and shows the after-tax interest and the end balance. Because tax takes a slice, the after-tax figure is what actually grows your savings, and is the number to compare against inflation.

Worked example

$10,000 at 4% with $200 a month added earns about $480 of interest before tax over the year. At a 30% RWT rate, about $144 is deducted, leaving roughly $336 of after-tax interest and an end balance near $12,800.

Related calculators

Savings Calculator: savings growth.
Term Deposit Calculator: term deposits.
Compound Interest Calculator: compounding.
Savings Goal Calculator: reach a goal.

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