A certificate of deposit pays a fixed rate for a fixed term, and breaking it early costs a stated penalty. That penalty is the mechanism that makes the fixed rate possible in the first place.
Banks price certificates against a known term
A bank that knows money will stay for a defined period can match it against lending or investments of similar duration without holding liquidity against sudden withdrawal.
That certainty is worth paying for, which is why certificate rates typically exceed the rate on an instantly accessible savings account.
If depositors could withdraw freely, the term commitment would be fictional and the bank would have to price the deposit as if it were on demand.
The penalty is calculated in months of interest
Early withdrawal penalties are usually expressed as a number of months of interest on the amount withdrawn, scaled to the length of the term.
Because the charge is defined in interest rather than principal, a certificate broken very early can return less than was deposited if little interest has accrued.
Institutions disclose the formula at account opening, and it varies enough between banks that it is a real point of comparison alongside the rate.
The break-even calculation is often favourable
If rates rise sharply after purchase, breaking a certificate and reinvesting at the higher rate can outperform holding it, once the penalty is subtracted.
The comparison is between the penalty as a one-off cost and the rate improvement multiplied by the remaining term.
A long remaining term and a large rate gap favour breaking, while a certificate close to maturity rarely justifies it because there is little time left to recover the charge.
Laddering reduces the need to break one at all
A ladder splits the money across certificates maturing at staggered intervals, so a portion reaches maturity regularly and can be spent or reinvested.
The structure provides periodic access without penalty while keeping most of the balance in longer terms that pay more.
It also averages the reinvestment rate across the cycle, which reduces the consequence of committing the entire balance at a single point in the rate cycle.
No-penalty and callable products change the trade
Some banks offer certificates that permit withdrawal after a short initial period without charge, in exchange for a lower rate than the standard product.
Callable certificates run the other way, paying more while allowing the issuer to redeem early, which transfers the rate risk to the depositor.
Both are variations on the same exchange: whoever holds the option to end the arrangement early gives up yield to the party who does not.