CD Calculator by Days

Calculate your certificate of deposit return based on the exact number of days you hold it. Enter a specific day count — 30, 90, 180, 270, or any custom number — to see precise interest earnings.

Your CD Earnings

Final Balance $10,511.62

Total Interest Earned $511.62

Initial Deposit: $10,000.00
Annual Percentage Yield (APY): 5.00%
CD Term: 12 months
Compounding Frequency: Monthly

What Is a CD Calculator by Days?

A CD calculator by days computes the interest and final balance on a certificate of deposit (CD) using an exact day count instead of months or years. This is useful for odd-term CDs, partial-year deposits, and situations where you need precision down to the calendar day. Banks internally calculate interest on a daily basis, so using exact days produces the most accurate projection of what your CD will earn.

Deposit & Days

Deposit Amount
APY Rate
Term Length
Compounding

Day Counter A = P × (1 + r/n)^n×t

Day-Exact Results

Interest Earned
Final Balance
Growth Chart

Key Benefits of Using a CD Calculator

Calculate CD returns for non-standard terms like 45 days, 90 days, 150 days, or 270 days that do not align neatly with monthly increments
Project the exact interest earned on a CD held for a specific number of calendar days — accurate to the penny
Estimate the payout on a CD you plan to close early by entering the actual number of days the deposit will be held
Compare returns on CDs with oddly stated terms, such as a 91-day Treasury-linked CD or a 182-day promotional CD

CD Interest Formula by Number of Days

The day-based CD formula converts the number of days into a fractional year for the compound interest equation. The term in years equals the number of days divided by 365. This conversion produces a precise result for any day count, whether it is 30 days, 180 days, or 547 days.

A = P × ( 1 + r / n ) ^{n × t}

Click or tap any variable to see what it means

A Balance After D Days: The total value of the CD after the specified number of days, including the original deposit and all interest accrued during that period.
P Opening Deposit: The principal amount deposited into the CD on day 1. Interest is calculated on this base amount for the specified number of days.
r Annual Rate: The yearly interest rate as a decimal. The rate is applied proportionally based on the fraction of the year represented by the day count.
n Compounding Frequency: The number of compounding events per year. Daily compounding (365) is the most common for day-count calculations since it matches the day-level precision.
D Number of Days: The exact calendar day count the CD is held. This is converted to years by dividing by 365: t = D ÷ 365. A 90-day CD equals 0.2466 years.

A 90-day CD at 5.00% compounded daily: t = 90 ÷ 365 = 0.2466 years. A = $10,000 × (1 + 0.05/365)^(365 × 0.2466) = $10,000 × (1.0001370)^90 = $10,124.06. The key conversion is D ÷ 365 for the time variable.

How to Use the CD Calculator by Days

Calculate your CD return for any exact number of days in 3 steps. The calculator converts your day count to a fractional year and runs the compound interest formula with daily compounding precision.

Enter Your Deposit and Rate

Type the dollar amount of your CD deposit and the annual percentage yield (APY) from your bank or credit union offer. The calculator will apply this rate proportionally based on the number of days you specify.

Specify the Exact Number of Days

Enter the CD term in months and the calculator converts it to days. For odd-term CDs, enter the closest month equivalent. Common day counts: 30 days (1 month), 60 days (2 months), 90 days (3 months), 180 days (6 months), 270 days (9 months), 365 days (1 year).

View Day-Precise Results

The calculator shows the total interest earned for the exact day count, the final balance, and a day-by-day growth chart. Adjust the day count to compare short and long holding periods.

Factors That Affect Day-Based CD Returns

Four factors determine how much a certificate of deposit earns over a specific number of days. Understanding each factor helps you project returns for any calendar period.

Exact Day Count

Every additional day adds a small increment of interest. A 90-day CD at 5.00% on $10,000 earns $124.06 in interest. Extending to 120 days earns $165.69 — adding $41.63 for the extra 30 days. Interest accrues every calendar day including weekends and holidays.

Day Count Convention (Actual/365)

Most US banks use the actual/365 day count convention, dividing the annual rate by 365 regardless of whether it is a leap year. Some institutions use actual/360, which produces a slightly higher daily rate (r ÷ 360 instead of r ÷ 365). Check your CD agreement for the convention used.

Short-Term vs. Long-Term Days

Short-term CDs (30 to 90 days) earn proportionally less total interest but may offer competitive rates for parking cash temporarily. A $50,000, 30-day CD at 5.00% earns $205.48 — enough to cover a monthly utility bill from interest alone.

Partial-Year Precision

Day-based calculations avoid the rounding errors that occur when converting odd terms to months. A 45-day CD is 0.1233 years (not 1.5 months). A 100-day CD is 0.2740 years (not 3.3 months). Using exact days produces results accurate to the penny.

Interest Earned by Day Count: $10,000 at 5.00% APY (Daily Compounding)

Daily365/yr

$2,840.25

Monthly12/yr

$2,833.59

Quarterly4/yr

$2,820.37

Annually1/yr

$2,762.82

Total interest earned on a $10,000 CD at 5.00% for different day counts

CD Calculation Examples by Days

These 4 examples show how a certificate of deposit earns interest over specific day counts. All examples use daily compounding (365/yr) to match the day-level precision of the calculation.

$10,000 CD — 90 Days at 5.00% (Daily)

Initial Deposit: $10,000
APY: 5.00%
Term: 3 Months
Compounding: Daily (365/yr)

Interest Earned $124.06

Final Balance $10,124.06

$10,000 CD — 270 Days at 5.00% (Daily)

Initial Deposit: $10,000
APY: 5.00%
Term: 9 Months
Compounding: Daily (365/yr)

Interest Earned $374.87

Final Balance $10,374.87