A certificate of deposit is a fixed lump sum at a fixed rate for a fixed term, which makes it the cleanest compound-interest case there is. Enter your deposit and rate (leave the monthly contribution at $0 for a classic CD), and this calculator shows the payoff with daily compounding preset, the schedule most banks use. Example, computed with the same engine: a $10,000 CD at 4.5% compounded daily grows to about $10,460 in 1 year and $11,445 in 3 years (monthly compounding would give $11,442, which is why you should compare CDs by APY, not by compounding schedule). Bank CDs are typically FDIC-insured up to the standard limits (FDIC deposit insurance). Nothing you type is uploaded, and there is no sign-up.
The background: APY vs APR · daily vs monthly compounding · how compound interest works
How CD interest compounds and pays
The CFPB describes a CD as a type of savings account where you agree to leave the money untouched for a set length of time (what is a certificate of deposit). That agreement is what makes the arithmetic simple: the principal does not move, the rate does not move, and the only variable is how often the interest compounds.
Most banks compound CD interest daily and credit it monthly or quarterly. Compounding is what turns a quoted nominal rate into an APY, and on a CD the whole spread between schedules is small. A $10,000 deposit at an illustrative 4.00% over 3 years:
| Compounding | Value after 3 years | APY |
|---|
| Daily | $11,274.89 | 4.081% |
| Monthly | $11,272.72 | 4.074% |
| Quarterly | $11,268.25 | 4.060% |
| Annually | $11,248.64 | 4.000% |
Daily beats annual by $26.25 across three years on $10,000, which is why the APY column is the one to shop with rather than the schedule itself. The frequency question is worked through in full on daily vs monthly compounding, and what an APY does and does not include is on APY vs APR.
One structural detail worth knowing: not every CD compounds. Some pay interest out to a linked account as it is earned rather than adding it back to the balance. When interest is disbursed, the balance never grows, so the return is simple interest on the original deposit. At an illustrative 4.00% over 3 years that is $1,200.00 of interest against $1,274.89 when the interest compounds daily instead. Same rate, same term, different mechanics.
Term and rate: what each one buys
A CD trades access for a locked rate, and the two dials you actually choose between are the term and the rate. This table isolates them. Every cell is a $10,000 deposit compounded daily at an illustrative rate; the rates are chosen to show the shape of the tradeoff and are not quotes:
| Illustrative rate | 1 year | 2 years | 3 years | 5 years |
|---|
| 3.50% | $10,356.18 | $10,725.05 | $11,107.05 | $11,912.36 |
| 4.00% | $10,408.08 | $10,832.82 | $11,274.89 | $12,213.89 |
| 4.50% | $10,460.25 | $10,941.68 | $11,445.27 | $12,523.05 |
Read it in two directions. Along a row, at a fixed 4.00%, stretching from a 1-year to a 3-year term adds $866.81. Down a column, at a fixed 3-year term, moving from 3.50% to 4.50% adds $338.22. Term buys time for compounding to work; rate buys a steeper curve.
The part no table can show is that a longer term also locks the rate for longer, and that cuts both ways depending on where rates go afterward. Nobody knows the direction in advance, which is the actual tradeoff a term decision involves.
Early withdrawal penalties, mechanically
Taking money out before maturity generally means paying a penalty, and the CFPB lists the penalty alongside the term and the rate as one of the three things to compare when shopping. Penalties are set in the account agreement and are usually expressed as a number of days or months of interest on the amount withdrawn.
Here is the mechanic, as an illustration only. Take a $10,000 deposit at an illustrative 4.00% compounded daily, on a CD whose agreement specifies a penalty of 180 days of simple interest: 10,000 × 0.04 × 180/365 = $197.26. Note that this penalty is a fixed amount tied to the deposit, while the interest you have earned grows with time. That is what produces the pattern below:
| Cashed out at | Balance | Interest earned | After the $197.26 penalty |
|---|
| 3 months | $10,100.50 | $100.50 | $9,903.24 |
| 6 months | $10,202.00 | $202.00 | $10,004.74 |
| 1 year | $10,408.08 | $408.08 | $10,210.82 |
| 2 years | $10,832.82 | $832.82 | $10,635.56 |
Exit at 3 months and the penalty exceeds everything earned, returning less than the original deposit. Exit at 6 months and it very nearly cancels the interest. By year 2 the penalty costs a modest slice of a much larger gain. Terms vary widely between institutions, and some agreements cap the penalty at the interest actually earned while others do not, so the figures above illustrate the shape rather than any particular product. The penalty schedule is in the account agreement, and it is worth reading before the money goes in rather than after.
CDs and savings accounts: the flexibility tradeoff
These two products answer different questions, and neither is better in the abstract. A savings account keeps the money available and lets the bank move the rate whenever it likes. A CD fixes the rate for the term and puts the money behind an early-withdrawal penalty. One protects access; the other protects the rate. Which fits depends on whether you need the money on a known date or on any date.
The comparison worth making is between APYs, because that single figure already accounts for each account's compounding schedule. At banks, both product types are typically covered by FDIC deposit insurance, which insures deposits to at least $250,000 per depositor, per insured bank, per ownership category, and covers checking, savings, money market deposit accounts, and CDs alike.
Laddering, described mechanically
A ladder splits one deposit across several CDs with staggered maturity dates instead of committing it all to a single date. The mechanics are easiest to see with round numbers: $25,000 divided into five $5,000 rungs, each at an illustrative 4.00% compounded daily, with terms running from one to five years.
| Term | Value at its own maturity |
|---|
| Rung 1 | 1 year | $5,204.04 |
| Rung 2 | 2 years | $5,416.41 |
| Rung 3 | 3 years | $5,637.45 |
| Rung 4 | 4 years | $5,867.50 |
| Rung 5 | 5 years | $6,106.95 |
Each rung matures a year after the one before it, so from the first anniversary onward some portion of the money comes free every twelve months. If each maturing rung is then rolled into a new five-year CD, the structure settles into a steady state: five five-year CDs, one maturing each year, at whatever rate is available on each renewal date.
What a ladder changes is the timing of access and the number of renewal dates you face, rather than the compound-interest math, which is identical inside every rung. Note that the rung values above are returned on five different dates, so they do not add up to anything comparable with a single lump-sum CD held for one term. To compare specific plans, run each rung through the calculator above with its own deposit, rate, and term.