Compare the same twelve months
6-month vs. 12-month CD: what renewal APY breaks even?
A six-month CD can advertise a higher APY and still leave you with less money after a year. The missing number is the yield available when you reinvest at maturity.
The answer depends on the second six months
Suppose you can deposit $10,000.00 at 4.50% APY for six months, or at 4.00% APY for twelve months. Under this model, the six-month option needs a renewal APY of about 3.5024% for the next six months to match the one-year CD.
A renewal above that threshold produces more gross interest; a renewal below it produces less. This is a comparison threshold, not a prediction of future rates or a recommendation to choose a particular term.
The CFPB recommends comparing a CD's term, rate and withdrawal penalty. Your need for access to the money can matter more than a small difference in modeled interest.
Worked example
Hold the starting deposit and end date constant
The twelve-month CD grows to $10,400.00, including $400.00 of gross interest.
The first six-month CD grows to $10,222.52. To compare the same twelve months, reinvest that entire amount for another six months. The second APY remains an assumption.
Both paths start with the same deposit and end after twelve modeled months. Comparing the six-month ending balance directly with the twelve-month balance would compare different holding periods.
Five possible renewal rates, five different outcomes
The initial six months always use 4.50% APY. Only the second six-month APY changes. The one-year comparison always ends at $10,400.00.
| Second six-month APY | Balance after twelve months | Total interest | Difference vs. one-year CD |
|---|---|---|---|
| 0.00% | $10,222.52 | $222.52 | −$177.48 |
| 2.00% | $10,324.24 | $324.24 | −$75.76 |
| 3.50% | $10,399.88 | $399.88 | −$0.12 |
| 4.00% | $10,424.97 | $424.97 | +$24.97 |
| 5.00% | $10,474.97 | $474.97 | +$74.97 |
At a rounded 3.50% renewal APY, the short-CD path ends about $0.12 below the one-year CD. The unrounded threshold is slightly higher. Weigh a few extra dollars of modeled interest against account terms, access needs and the effort of renewing.
How to calculate the break-even renewal APY
Write APYs as decimals: 4.50% becomes 0.045, and 4.00% becomes 0.04. For two equal six-month periods:
Here, 1.042 ÷ 1.045 − 1 = 0.0350239234, or approximately 3.5024% APY.
Set the two paths equal: P × (1 + first APY)½ × (1 + renewal APY)½ = P × (1 + one-year APY). The starting deposit P cancels. The threshold is the same for other deposit sizes under these assumptions, although the dollar difference changes.
APY is already an annual effective yield. Do not add compounding to it again. The CFPB's APY calculation rules use the account's term and day count; this educational model uses months divided by twelve, matching our CD calculator.
Reproduce the comparison with the CD calculator
- Enter $10,000.00, 4.00% APY and twelve months. Record the $10,400.00 ending value.
- Enter $10,000.00, 4.50% APY and six months. Record the $10,222.52 ending value.
- Use the six-month ending value as a new deposit, enter a possible renewal APY and another six-month term, then compare with the twelve-month value.
The table keeps full precision between periods and rounds displayed results only. Re-entering a displayed balance rounded to cents can create a small rounding difference. The calculator models each term separately; it does not currently solve a renewal threshold or renew a bank account.
Check the terms before using the result
- Renewal and access: check the maturity notice, grace period, automatic-renewal terms and how the new rate will be set. Regulation DD's account-disclosure requirements cover relevant time-account terms; do not assume every institution uses the same grace period.
- Reinvestment: the full principal and interest are reinvested immediately. A transfer delay, interest payout or new minimum deposit can change the comparison.
- Costs and taxes: these examples exclude fees, penalties and taxes. The IRS generally treats CD interest as taxable interest; this table shows gross amounts.
- Product scope: these are plain fixed-rate deposit scenarios held to maturity. Callable, brokered, stepped-rate and other special CDs can require different modeling. Check the issuing institution's insurance coverage and account agreement.
The calculation answers one narrow question: what second-period APY would make two modeled balances equal? It does not measure inflation, predict rates or decide which account fits your circumstances.
Common questions
Frequently asked questions
Does a higher six-month CD APY beat a lower one-year APY?
Not automatically. Compare both choices over the same time horizon. The six-month choice also depends on the APY available for the next six months and whether you reinvest all the proceeds.
What renewal APY breaks even in this example?
With a hypothetical 4.50% APY for the first six months and 4.00% APY for a full year, the second six-month APY must be about 3.5024% to match the one-year balance. This assumes immediate full reinvestment and equal half-year periods, before taxes or fees.
Is the renewal APY guaranteed when I open the first CD?
This comparison does not assume a guaranteed renewal APY. Read the account agreement and the renewal notice. The APY offered at maturity may differ from the first term’s APY.
Does this calculation include taxes or an early-withdrawal penalty?
No. It compares gross maturity values for CDs held to maturity. Taxes, fees, withdrawal penalties, exact day counts, required interest payouts, and time out of the market can change the result.