The advertised yield is not what you keep
A 4.25% APY on $20,000 earns $850 over a year. That is the number banks advertise, and it is accurate as far as it goes.
Interest is taxed as ordinary income, not at the lower capital gains rate. At a 24% marginal rate, $204 of that $850 goes to tax, leaving $646. Your effective yield is 3.23%, not 4.25%.
Then inflation. At 3%, the real return on that after-tax yield is about 0.22%. You began with $20,000 and ended with roughly $20,045 in purchasing power — you did not lose ground, but a year of holding produced almost nothing in real terms.
This is the honest picture of cash savings, and it is why the calculator shows it. The nominal balance rising creates a strong impression of progress that the real return does not support.
Which is a feature, not a failure
None of this means CDs and savings accounts are bad. It means they are doing a different job than investing.
Their job is preservation and liquidity. Federal deposit insurance covers up to $250,000 per depositor per bank, the balance cannot fall, and the money is available when you need it. For an emergency fund or a house deposit two years out, roughly matching inflation with zero risk is exactly the right outcome.
The mistake is using them for long-horizon money. Over thirty years, a 0.22% real return compounds to almost nothing while a diversified portfolio has historically grown substantially. Cash is the right tool for short horizons and the wrong one for long ones — the reverse of what risk-averse instincts often suggest.
CDs versus high-yield savings
A CD locks your money for a fixed term at a fixed rate, with an early withdrawal penalty — commonly three to six months of interest — if you break it. A high-yield savings account is fully liquid but its rate floats and can be cut at any time.
The tradeoff is straightforward. CDs make sense when you are confident you will not need the money and want to lock a rate you expect to fall. Savings accounts make sense when you might need the money or expect rates to rise.
A CD ladder splits the difference: divide the money across CDs maturing at staggered intervals, so a portion becomes available regularly and can be reinvested at prevailing rates. You give up a little yield relative to a single long CD in exchange for much better access and less rate-timing risk.
Also compare against Treasury bills. They often yield similarly, are backed by the federal government, and — importantly — their interest is exempt from state and local income tax. In a high-tax state that exemption can outweigh a slightly lower headline rate.
Details that change the outcome
Compare APY, not interest rate. APY already incorporates compounding, so it is the figure that lets you compare accounts fairly. A 4.00% rate compounded daily and a 4.05% rate compounded annually are close to identical.
Watch for teaser rates and balance caps. Some accounts pay a headline rate only for an introductory period, or only on balances up to a threshold, with a much lower rate above it.
Online banks consistently pay far more than large branch-based banks, often by several percentage points. The deposit insurance is identical. This is one of the few places in personal finance offering a meaningful, risk-free improvement for about twenty minutes of work.
Finally, interest is taxable in the year it is credited, even inside a CD you have not touched. You will receive a 1099-INT and owe tax on interest you have not yet been able to spend.
Frequently asked questions
- Is CD interest taxable?
- Yes, as ordinary income at your marginal rate, in the year it is credited. For multi-year CDs that means owing tax annually on interest you cannot access until maturity.
- What happens if I withdraw from a CD early?
- Most charge a penalty of three to six months of interest, sometimes more on longer terms. Some no-penalty CDs exist at slightly lower rates.
- Is my money safe?
- In the US, FDIC insurance covers up to $250,000 per depositor, per insured bank, per ownership category. Credit unions have equivalent NCUA coverage. Keep balances at any single institution below the limit.
- Should I use a CD or invest in the market?
- It depends entirely on the timeline. Money needed within two or three years belongs in cash-like accounts, where a market drop cannot force a loss. Money with a horizon beyond five to ten years has historically done far better invested, and cash's near-zero real return becomes the greater risk.