18 Month CD Calculator

What an 18 month certificate of deposit is

An 18 month certificate of deposit is a savings product that holds a lump sum for one and a half years at a fixed rate. You hand the bank a deposit, agree to leave it alone until the maturity date, and the bank returns the deposit plus the interest it promised. The Consumer Financial Protection Bureau describes a CD as a savings account with a set term and a penalty for withdrawing early, and it tells shoppers to compare the term, the rate, and the penalty together.

Eighteen months is a middle rung. It sits above the 6 and 12 month terms that chase whatever rate is available right now, and below the 3 to 5 year terms that lock money away for longer than most households want. Banks often price the middle of the curve close to the top, which is why the 18 month term shows up in so many rate tables.

CDs sold by banks carry FDIC insurance up to 250,000 dollars per depositor, per insured bank, for each account ownership category. Credit union share certificates carry the same limit through the NCUA. Within those limits the payout does not depend on the stock market or on the bank staying healthy, because the insurance covers principal plus accrued interest.

How the 18 month payout is calculated

The standard compound interest formula drives the whole calculation: A = P(1 + r/n)^(nt). P is the initial deposit, r is the annual rate as a decimal, n is the number of compounding periods per year, and t is the term in years. For this calculator t is fixed at 1.5, because 18 months is one and a half years. The exponent nt is therefore 1.5n, which is 27 periods at monthly compounding and 547.5 periods at daily compounding.

When a bank quotes an APY instead of a rate, the compounding is already folded in. The calculator then grows the deposit at the quoted yield for one and a half years: A = P(1 + APY)^1.5. Both roads land on the same maturity if the rate and the APY describe the same compounding schedule, which is why the calculator accepts either input.

Take 10,000 dollars at 4.50 percent APY. The maturity is 10,000 times 1.045 raised to the power 1.5, which is 10,682.54 dollars. The interest is the maturity minus the deposit, or 682.54 dollars. Change only the compounding and the numbers shift by a few dollars, which the next sections show in detail.

The deposit size scales the payout in a straight line at a fixed APY. The table below holds the same 4.50 percent APY and the same 18 month term and walks the deposit up a ladder.

Every row earns exactly 6.83 percent of the deposit over the term, because a fixed APY turns the deposit up by the same factor. Note that the 100,000 dollar row still fits inside the 250,000 dollar FDIC limit at a single bank.

Worked example: 10,000 dollars at 4.50 percent APY

This first example follows a 10,000 dollar deposit at 4.50 percent APY through the full term. The balance compounds annually at the quoted yield, and the interest earned grows each month because the base it earns on keeps rising.

At the halfway mark the deposit has earned 222.52 dollars, at 12 months it has earned 450.00 dollars, and at maturity the interest reaches 682.54 dollars. The second half of the term pays 232.54 dollars of interest against 222.52 in the first half, and the gap comes from compounding on interest already credited.

APY versus the stated rate

Banks advertise the APY because it is the number that compares cleanly across offers. APY folds the annual rate and the compounding frequency into one yield, so a 4.50 percent rate compounded daily and a 4.55 percent rate compounded annually can be judged at a glance. The APY on a 4.50 percent rate compounded daily is (1 + 0.045/365)^365 minus 1, which is 4.60 percent.

On a term as short as 18 months the frequency matters, but only by a handful of dollars. The table runs a 10,000 dollar deposit at a 4.50 percent annual rate across five schedules for the full 1.5 year term.

Daily compounding beats annual by 15.72 dollars on a 10,000 dollar deposit over 18 months. That gap is real but small, so a bank offering 4.40 percent daily can lose to a bank offering 4.50 percent annual. Compare APY to APY and the compounding question answers itself.

A larger deposit widens the gap in dollar terms. At 25,000 dollars and a 4.50 percent rate compounded daily, the 18 month maturity is 26,745.65 dollars and the interest is 1,745.65 dollars, versus 1,706.34 dollars with annual compounding at the same rate.

Adding a monthly contribution

Most CDs accept new money only at opening, but a few accounts let you add funds, and some savers pair a CD with a monthly transfer into the same bank. The calculator has an optional contribution field for that case. It adds the contribution at the end of each month and pays the same effective monthly rate on it, which is the standard way to value a series of equal deposits.

Start with 10,000 dollars at 4.50 percent APY and add 100 dollars a month. Over 18 months you deposit 11,800.00 dollars in total, and the balance compounds to 12,539.88 dollars at maturity. The interest earned is 739.88 dollars, of which 57.34 dollars comes from the contributions themselves rather than the opening deposit.

The contributions earn less than the opening deposit because they arrive late. The final 100 dollar deposit sits in the account for a single month and earns about 37 cents, while the opening 10,000 dollars earns the full 682.54 dollars. Extra deposits still help, but money placed early does most of the work, which is the same logic that makes a longer term worth more.

What 18 month rates look like in 2026

Published rate surveys give the context for judging any offer. The FDIC publishes national average rates each month, and its October 2026 table lists 1.76 percent for 12 month CDs and 1.55 percent for 24 month CDs. The FDIC posts on the standard tenors and skips 18 months, so the nearest published averages bracket the term. Those national averages drag on small branch banks, so the top of the market sits far above them.

Private surveys of competitive banks show the spread. Bankrate's November 2026 ranking of 18 month CDs put Bread Savings at 4.85 percent APY and Popular Direct at 4.80 percent APY, with a cluster of online banks between 4.30 and 4.70 percent. Forbes Advisor's October 2026 survey found top 18 month APYs near 4.50 percent. A useful rule from those tables: an 18 month offer under 3 percent is well behind the market in late 2026, and one at 4.50 percent or better is near the top.

Rate context moves with the Federal Reserve cycle, so treat any figure here as a snapshot for its stated month. The formula and the calculator stay valid whatever the rate does, and the FDIC insurance limit applies at every point on the curve.

Early withdrawal penalties and the 547 day term

An 18 month CD runs about 547 days, though the bank's disclosure sets the exact day count and maturity date. Cash out before that date and the bank charges an early withdrawal penalty, usually stated as a number of months of interest. The SEC's Investor.gov lists the penalty terms as a required part of the CD disclosure and warns that redeeming early can cost part of the interest you earned.

For an 18 month term, 6 months of interest is the common penalty at online banks. Under the simple convention of months times rate over 12, a 6 month penalty on 10,000 dollars at 4.50 percent is 225.00 dollars, about a third of the 682.54 dollars the full term pays. A withdrawal in the first months can exceed the interest earned to that point and cut into principal, which is why the penalty belongs in your comparison before you open the account.

At maturity most banks roll the CD into a new term automatically unless you act during the grace period, which typically runs 7 to 10 days after the maturity date. Mark the date and decide during the window whether to take the cash or renew at the then current rate.

Where an 18 month CD sits next to other safe options

A high yield savings account pays a variable rate and lets you withdraw at any time, so it fits emergency money. The 18 month CD trades that flexibility for a locked rate, which pays off if rates fall during the term and costs you the penalty if you need the cash early. A common split keeps the emergency fund in savings and moves known future expenses, such as a tuition bill due in 2028, into the CD.

TreasuryDirect sells Treasury bills with maturities from 4 to 52 weeks at a $100 minimum, and state and local tax exemptions can favor bills over bank interest for some filers. Bills mature too fast to cover an 18 month horizon in one purchase, though rolling them is an alternative for savers who want the liquidity. A CD ladder with rungs at 6, 12, and 18 months splits the difference: money frees up on a schedule while the longest rung still captures the middle of the rate curve.

Enter your own deposit, APY, and any planned monthly additions above to see the exact 18 month payout. All calculations run in your browser and no data leaves the page.