Yes, a CD at an FDIC-insured bank is safe up to $250,000 per depositor, per bank, per ownership category, and that coverage protects your principal even if the bank itself fails. The insurance applies automatically the moment you open the account, with no paperwork or fee required, and it covers accrued interest as well as the original deposit, not just the amount you first put in. Suppose you deposit $10,000 in a 12-month CD at 4.50% APY, compounded daily: the account matures at $10,450.00 regardless of the bank's own financial condition, because the FDIC guarantee stands behind that number, not the bank's balance sheet. Two things can still leave you behind despite that guarantee: an early withdrawal penalty that exceeds the interest you have earned, which can dip into principal on a CD closed very early, and a fixed rate that trails inflation over a multi-year term, which erodes purchasing power without ever changing the account balance itself.

What is the minimum to open a CD?

Minimums commonly run $500 to $2,500 at traditional banks, though many online banks require no minimum deposit at all and will open a CD with any amount you choose. The minimum exists because a bank incurs a fixed administrative cost to open and service any account, so a small floor keeps that cost from outweighing the deposit itself; below it, the bank simply will not open the account. On a $500 minimum deposit at 4.50% APY for 12 months, compounded daily, the CD matures at $522.50, a $22.50 gain — a real but modest return that illustrates why minimums matter less than the rate once you clear them. Jumbo CDs sit at the opposite end, typically requiring $100,000 or more, and sometimes paying a slightly higher rate in exchange for that larger, single-lump-sum commitment. Whatever the minimum, it applies only once, at opening, since a standard CD does not accept further deposits during its term.

Can you add money to a CD after opening it?

Usually not — a standard CD accepts one lump-sum deposit at opening and does not allow further contributions for the rest of the term, unlike a savings account you can keep feeding indefinitely. The restriction exists because the bank prices the CD, and manages its own funding, around a known, fixed amount for a known, fixed period; letting the balance grow unpredictably would undermine the fixed-rate promise that defines the product. If you deposit $10,000 at opening in a 12-month CD at 4.50% APY, compounded daily, that $10,000 is the entire base the account grows from, maturing at $10,450.00 with no room to add another dollar along the way. Add-on CDs are the exception: a small number of banks offer this specific variant, which does permit additional deposits during the term, usually within stated limits. They are uncommon rather than standard, so check your particular account disclosure before assuming you can top up a CD you already opened.

What happens if I need the money before maturity?

You can withdraw the money early, but the bank charges an early withdrawal penalty, calculated as a set number of months of simple interest on the principal rather than on whatever balance you have actually accrued. The penalty compensates the bank for the funding certainty it gave up, and it is deducted first from the interest you have earned before touching anything else. Suppose you open a $10,000 CD at a 4.50% rate, compounded daily, for a 12-month term, with a 6-month penalty for early withdrawal. Six months in, the balance has grown to about $10,227.54, or $227.54 in interest earned so far. The penalty is 10,000 × 0.045 × (6 ÷ 12) = $225.00. Subtract it from the interest earned and you keep just $2.54 in net interest, walking away with $10,002.54 — barely ahead of your deposit. If the penalty exceeds what you have earned, the shortfall comes directly out of your principal, the one scenario where a CD returns less than you deposited.

Does a CD's rate ever change during the term?

Not on a standard fixed-rate CD — the rate quoted at opening is locked for the entire term and cannot move regardless of what happens to market rates in the meantime, in either direction. That immovability is the defining feature of the product: the bank is trading a rate it cannot raise for you in exchange for a rate it also cannot lower, and the fixed-rate guarantee is what lets it offer a higher starting number than a variable account typically does. On a $10,000 CD locked at 4.50% APY, compounded daily, for 12 months, the maturity value is $10,450.00 whether market rates rise, fall, or hold steady during that year — the outcome is fixed the moment you fund the account. Bump-up and step-up CDs are the named exceptions, allowing a rate increase on specific, pre-disclosed terms, and a small number of variable-rate CDs track an index directly; a plain fixed-rate CD, the most common structure, simply does not move.

Is a brokered CD different from a bank CD?

A brokered CD carries the same FDIC insurance as a bank CD, since the underlying deposit still sits at an FDIC-insured bank, but you buy and, if needed, sell it through a brokerage account instead of dealing with the bank directly. The mechanism differs at the exit: a standard bank CD charges a fixed early withdrawal penalty for leaving early, while a brokered CD is instead sold on a secondary market at whatever price it currently commands, which moves with prevailing interest rates the way a bond price does. On $10,000 placed in either a bank CD or a brokered CD at 4.50% APY for 12 months, held to maturity, both mature at the identical $10,450.00, since the insurance and the underlying rate are the same. The difference only shows up if you exit early: a brokered CD sold before maturity can fetch more or less than you paid, unlike the bank CD's predictable, fixed penalty.

BasicsCD fundamentals10 分で読めます

What Is a CD (Certificate of Deposit) and How Does It Work?

かんたん定期預金計算フル機能ツール

満期時: $10,450.00
利息: $450.00

預入金額

金利 (APY)

預入期間

$10,000.00 for 1 year, compounded daily. Runs in your browser.

A certificate of deposit is a time deposit: you leave a fixed sum with a bank for a fixed term, and the bank pays a fixed rate that is normally higher than a savings account. Withdraw early and you pay a penalty. Deposits are FDIC-insured up to $250,000 per depositor, per bank.

公開日 2025年9月16日 · 最終確認日 2026年7月22日 · 執筆・事実確認 Ali Raza · 当サイトの算出方法 · 用語の解説

How a CD actually works

A certificate of deposit is a loan you make to a bank for a fixed term at a fixed rate. You choose an amount and a length; the bank commits to a rate it cannot change for as long as the CD stays open. That immovability is the entire product. A savings account's rate can move the week after you fund it, in either direction. A CD's cannot, and almost everything else about the product — the early withdrawal penalty above all — exists to let the bank make that promise.

Interest is credited on the schedule set out in your account disclosure, most often daily or monthly, and each credited amount joins the principal and starts earning interest of its own for the rest of the term. That is compounding, and the formula behind it is the standard one: A = P(1 + r/n)^(nt), where P is the principal, r the nominal annual rate, n the number of compounding periods per year, and t the term in years. Nothing about a CD's growth happens outside that formula — no bonus tiers, no fee drag, just principal compounding at a locked rate for a fixed stretch of time.

A worked example: $10,000 for 12 months

Suppose a bank quotes a 12-month CD at 4.50% APY, compounded daily, and you deposit $10,000. Because APY is already the effective annual yield, the daily compounding is baked into that 4.50% figure, so the balance after one year is simply 10,000 × 1.045 = $10,450 — $450 in interest on a $10,000 deposit over a 12-month term, or an average of $37.50 a month. Back out the daily compounding and the nominal rate behind that APY works out to about 4.40%, which is the figure a disclosure would label as the 'interest rate' rather than the APY.

What you give up: liquidity, not principal safety

Money in a CD is not gone and it is not exposed to the bank's fortunes — it is simply unavailable on your own schedule. Close it before the maturity date and the bank charges an early withdrawal penalty, standardly expressed as a set number of months of interest on the principal, not on the balance you have actually earned. If you have not yet earned that much interest, the shortfall comes out of your deposit itself, which is the one scenario in which a CD can hand back less than you put in.

Terms under 12 months typically carry a penalty of about 3 months of interest.
Terms of 1 to 4 years usually carry around 6 months.
Terms of 5 years or more often carry 9 to 12 months.

One lump sum, not a running balance

A CD is normally funded once, at opening, and that is by design rather than an oversight. Unlike a savings account, you generally cannot add money to one later — if you want to save more, you open another CD or wait for this one to mature and redeposit. Minimum opening deposits commonly run $500 to $2,500 at traditional banks, though many online banks have no minimum at all, and jumbo tiers starting around $100,000 sometimes carry a modest rate premium. Whatever the entry point, expect a single deposit, a single term and a single rate for the account's whole life.

Deciding whether a CD is the right container

A CD suits money that has a deadline and no tolerance for loss: a house deposit eighteen months out, a tax bill due next spring, the fixed-income portion of a retirement portfolio. It is a poor fit for money you might need without warning, since the early withdrawal penalty can erase months of interest, and a poor fit for very long horizons where a fixed rate risks trailing inflation or other assets over time.

Opening a long CD is also an implicit bet that rates will hold steady or fall, because you cannot capture a later rate increase without breaking the CD and paying for the privilege. If you have no strong view on where rates are headed — and most savers do not — spreading money across several maturities is a more defensible default than concentrating it all in one term.

Treasury bills are worth a passing comparison, since they carry similar backing — the full faith and credit of the federal government rather than deposit insurance — and often similar terms. The practical differences are smaller minimums and easier laddering with a CD, against interest that is exempt from state income tax with a T-bill, a real edge for savers in high-tax states even though it rarely decides the question on its own.

Where people get this wrong

Treating a CD like an emergency fund, then paying a penalty to reach money that needed to stay liquid in the first place.
Comparing one bank's APY against another bank's nominal rate and concluding the nominal number is competitive, when the two are not directly comparable.
Missing the maturity notice and letting the CD auto-renew into the bank's current standard rate, which is frequently lower than the rate originally locked in.
Opening several CDs at one bank without checking that the combined balance, plus the interest they are accruing, still sits under the $250,000 FDIC insurance limit.

How CD interest is taxed

Interest on a CD is taxable in the year it is credited to your account, whether you withdraw it or let it ride toward maturity — including on multi-year CDs where you never touch a dollar until the term ends. Your bank reports the amount to you and to the IRS on Form 1099-INT. The main exception is a CD held inside a tax-advantaged account such as an IRA, where that account's own distribution rules apply instead of ordinary interest-income treatment.

Bank CDs, credit union certificates, and brokered CDs

A bank CD and a credit union 'share certificate' are the same product wearing a different name — the credit union version is insured by the NCUA rather than the FDIC, on the same per-member, per-institution, per-ownership-category basis. Rates at credit unions are sometimes a touch higher because the institution is member-owned rather than shareholder-owned, though membership eligibility is the price of entry.

A brokered CD is a third variant, bought through a brokerage account rather than directly from the issuing bank. The underlying deposit is still FDIC-insured through that bank, but instead of paying an early withdrawal penalty to exit early, you sell the CD on a secondary market at whatever price it currently commands — which can land above or below what you paid, since a brokered CD trades more like a bond than a fixed bank product once it is issued.

よくある質問

Yes, a CD at an FDIC-insured bank is safe up to $250,000 per depositor, per bank, per ownership category, and that coverage protects your principal even if the bank itself fails. The insurance applies automatically the moment you open the account, with no paperwork or fee required, and it covers accrued interest as well as the original deposit, not just the amount you first put in. Suppose you deposit $10,000 in a 12-month CD at 4.50% APY, compounded daily: the account matures at $10,450.00 regardless of the bank's own financial condition, because the FDIC guarantee stands behind that number, not the bank's balance sheet. Two things can still leave you behind despite that guarantee: an early withdrawal penalty that exceeds the interest you have earned, which can dip into principal on a CD closed very early, and a fixed rate that trails inflation over a multi-year term, which erodes purchasing power without ever changing the account balance itself.
Minimums commonly run $500 to $2,500 at traditional banks, though many online banks require no minimum deposit at all and will open a CD with any amount you choose. The minimum exists because a bank incurs a fixed administrative cost to open and service any account, so a small floor keeps that cost from outweighing the deposit itself; below it, the bank simply will not open the account. On a $500 minimum deposit at 4.50% APY for 12 months, compounded daily, the CD matures at $522.50, a $22.50 gain — a real but modest return that illustrates why minimums matter less than the rate once you clear them. Jumbo CDs sit at the opposite end, typically requiring $100,000 or more, and sometimes paying a slightly higher rate in exchange for that larger, single-lump-sum commitment. Whatever the minimum, it applies only once, at opening, since a standard CD does not accept further deposits during its term.
Usually not — a standard CD accepts one lump-sum deposit at opening and does not allow further contributions for the rest of the term, unlike a savings account you can keep feeding indefinitely. The restriction exists because the bank prices the CD, and manages its own funding, around a known, fixed amount for a known, fixed period; letting the balance grow unpredictably would undermine the fixed-rate promise that defines the product. If you deposit $10,000 at opening in a 12-month CD at 4.50% APY, compounded daily, that $10,000 is the entire base the account grows from, maturing at $10,450.00 with no room to add another dollar along the way. Add-on CDs are the exception: a small number of banks offer this specific variant, which does permit additional deposits during the term, usually within stated limits. They are uncommon rather than standard, so check your particular account disclosure before assuming you can top up a CD you already opened.
You can withdraw the money early, but the bank charges an early withdrawal penalty, calculated as a set number of months of simple interest on the principal rather than on whatever balance you have actually accrued. The penalty compensates the bank for the funding certainty it gave up, and it is deducted first from the interest you have earned before touching anything else. Suppose you open a $10,000 CD at a 4.50% rate, compounded daily, for a 12-month term, with a 6-month penalty for early withdrawal. Six months in, the balance has grown to about $10,227.54, or $227.54 in interest earned so far. The penalty is 10,000 × 0.045 × (6 ÷ 12) = $225.00. Subtract it from the interest earned and you keep just $2.54 in net interest, walking away with $10,002.54 — barely ahead of your deposit. If the penalty exceeds what you have earned, the shortfall comes directly out of your principal, the one scenario where a CD returns less than you deposited.
Not on a standard fixed-rate CD — the rate quoted at opening is locked for the entire term and cannot move regardless of what happens to market rates in the meantime, in either direction. That immovability is the defining feature of the product: the bank is trading a rate it cannot raise for you in exchange for a rate it also cannot lower, and the fixed-rate guarantee is what lets it offer a higher starting number than a variable account typically does. On a $10,000 CD locked at 4.50% APY, compounded daily, for 12 months, the maturity value is $10,450.00 whether market rates rise, fall, or hold steady during that year — the outcome is fixed the moment you fund the account. Bump-up and step-up CDs are the named exceptions, allowing a rate increase on specific, pre-disclosed terms, and a small number of variable-rate CDs track an index directly; a plain fixed-rate CD, the most common structure, simply does not move.
A brokered CD carries the same FDIC insurance as a bank CD, since the underlying deposit still sits at an FDIC-insured bank, but you buy and, if needed, sell it through a brokerage account instead of dealing with the bank directly. The mechanism differs at the exit: a standard bank CD charges a fixed early withdrawal penalty for leaving early, while a brokered CD is instead sold on a secondary market at whatever price it currently commands, which moves with prevailing interest rates the way a bond price does. On $10,000 placed in either a bank CD or a brokered CD at 4.50% APY for 12 months, held to maturity, both mature at the identical $10,450.00, since the insurance and the underlying rate are the same. The difference only shows up if you exit early: a brokered CD sold before maturity can fetch more or less than you paid, unlike the bank CD's predictable, fixed penalty.

出典

上記のルールや上限は、二次的な要約ではなく、それを定めている機関の資料から直接引用しています。

Regulation DD, 12 CFR Part 1030 — Truth in Savings — CFPB
Deposit Insurance At A Glance — coverage limits — FDIC
About Form 1099-INT, Interest Income — IRS
Certificates of deposit — brokered CDs investor guidance — FINRA

What Is a CD (Certificate of Deposit) and How Does It Work?

How a CD actually works

A worked example: $10,000 for 12 months

What you give up: liquidity, not principal safety

One lump sum, not a running balance

Deciding whether a CD is the right container

Where people get this wrong

How CD interest is taxed

Bank CDs, credit union certificates, and brokered CDs

よくある質問

出典

関連するガイド

How Much Money Do You Need to Open a CD?

How Compound Interest Grows Your CD Savings Over Time

Are CDs FDIC Insured? Understanding Deposit Safety

ご自身のCDがいくら増えるかを確認

How a CD actually works

A worked example: $10,000 for 12 months

What you give up: liquidity, not principal safety

One lump sum, not a running balance

Deciding whether a CD is the right container

Where people get this wrong

How CD interest is taxed

Bank CDs, credit union certificates, and brokered CDs

よくある質問

Is a CD safe?

What is the minimum to open a CD?

Can you add money to a CD after opening it?

What happens if I need the money before maturity?

Does a CD's rate ever change during the term?

Is a brokered CD different from a bank CD?

出典

関連するガイド

How Much Money Do You Need to Open a CD?

How Compound Interest Grows Your CD Savings Over Time

Are CDs FDIC Insured? Understanding Deposit Safety

ご自身のCDがいくら増えるかを確認