How Interest Is Calculated On A Savings Account

A savings rate is a headline that conceals several mechanical choices. Those choices determine what actually lands in the account across a year.

Accrual and crediting are separate events

Interest usually accrues daily on the balance held, calculated as the rate divided across the year and applied to whatever sits in the account that day.

Crediting is when the accrued amount is actually added, which may be monthly, annually or on maturity depending on the product.

The distinction matters because interest only begins earning interest itself once it has been credited.

Compounding frequency changes the outcome

An account crediting monthly adds interest that then earns interest for the remaining months, producing slightly more across a year than annual crediting at the same rate.

The effect is modest at low rates and small balances and grows with both, which is why it is worth checking on larger sums.

Comparison figures that express an equivalent annual rate exist precisely to make this comparable, though the terminology varies by jurisdiction.

Daily balance calculation rewards timing

Where interest accrues on the daily balance, money deposited earlier in the month earns for more days, and a withdrawal reduces accrual immediately.

Some products instead use a minimum monthly balance or a balance on a particular date, which changes the incentive substantially.

Reading which method applies is the only way to know whether the timing of deposits within a month matters at all.

Tiered rates apply differently between products

Accounts paying tiered rates by balance either apply the higher rate to the whole balance once a threshold is passed, or only to the portion above it.

Those two structures produce noticeably different outcomes near a threshold, and neither is signalled by the advertised rate alone.

The same applies to accounts paying a bonus rate on the first portion of a balance, where the effective rate falls as the balance grows.

Deductions and reporting vary by system

Interest may be paid gross or with tax deducted at source depending on the country, and the treatment of savings income differs widely.

These rules vary by jurisdiction and change over time, so the net position on an advertised rate is not something that can be assumed from the headline figure.

Where interest is credited annually on an anniversary rather than at a tax year end, the timing can also affect which reporting period it falls into.