Daily Interest Calculator
Calculate interest earned or accrued on a daily basis. Perfect for savings accounts, certificates of deposit, money market accounts, loans, and credit card balances. Supports both simple and compound interest with multiple day count conventions.
Daily Interest
Calculate interest earned per day
Quick Examples:
Interest Calculation Results
Detailed Breakdown
| Day | Interest | Cumulative | Balance |
|---|---|---|---|
| 1 | $1.3699 | $1.37 | $10001.37 |
| 2 | $1.3699 | $2.74 | $10002.74 |
| 3 | $1.3699 | $4.11 | $10004.11 |
| 4 | $1.3699 | $5.48 | $10005.48 |
| 5 | $1.3699 | $6.85 | $10006.85 |
| 6 | $1.3699 | $8.22 | $10008.22 |
| 7 | $1.3699 | $9.59 | $10009.59 |
| 8 | $1.3699 | $10.96 | $10010.96 |
| 9 | $1.3699 | $12.33 | $10012.33 |
| 10 | $1.3699 | $13.70 | $10013.70 |
A $10,000.00 deposit at 5% annual rate earns $1.37 per day. Over 30 days, you'll earn $41.10 in simple interest, resulting in an ending balance of $10,041.10.
Editorial & Review Information
Reviewed on: 2026-02-27
Published on: 2025-12-04
Author: LumoCalculator Editorial Team
Editorial review: We reviewed formula logic, day-count explanations, and source reliability to keep this page clear for practical planning use.
Purpose and scope: This calculator supports educational estimation and planning for deposits, savings, and borrowing scenarios. It is not a loan contract, rate quote, or regulatory disclosure.
Financial Disclaimer
Results are model estimates. Actual interest charged or paid can differ due to lender-specific contracts, billing cycles, compounding policy, fees, grace-period rules, and jurisdictional disclosure requirements.
Use Scenarios
Savings projection
Estimate how much interest a balance may generate over a short holding period before moving funds.
Loan accrual check
Compare expected daily accrual with statement figures to understand the impact of timing and payment dates.
Convention comparison
Test Actual/365 vs Actual/360 to see how day-count conventions can change accrued interest for the same nominal annual rate.
Formula Explanation
Simple daily interest
Interest = P x (r / D) x d
- P: principal balance
- r: annual nominal rate (decimal form)
- D: day-count denominator (365, 366, or 360)
- d: number of accrual days
Daily compounding model
A = P x (1 + r / D)^d
Compound mode applies interest on principal plus prior accrued interest. For short periods, the difference versus simple mode is usually modest but grows with time and rate.
Effective annual rate context
EAR = (1 + r / D)^D - 1
EAR provides a comparable annualized rate that includes compounding effects and helps normalize offers with different compounding frequencies.
Example Cases
Case 1: Savings accrual
Principal $12,000, annual rate 4.8%, 45 days, Actual/365, simple mode. Estimated interest = 12,000 x (0.048 / 365) x 45 = $71.01.
Case 2: Revolving balance
Principal $3,500, annual rate 22%, 30 days, Actual/365, simple proxy. Estimated accrual = 3,500 x (0.22 / 365) x 30 = $63.29.
Case 3: Convention impact
Principal $50,000, annual rate 5.2%, 90 days. Actual/365 simple interest = $641.10; Actual/360 simple interest = $650.00; difference = $8.90.
Boundary Conditions
Typical Interest Rates by Product
| Application | Typical Rate | Convention |
|---|---|---|
| Savings Account | 0.5% - 5% | Actual/365 |
| Money Market | 4% - 5.5% | Actual/360 |
| Certificate of Deposit | 4% - 5.5% | Actual/365 |
| Credit Card | 15% - 25% | Actual/365 |
| Personal Loan | 6% - 15% | Actual/365 |
| Treasury Bills | 4% - 5.5% | Actual/360 |
Day Count Conventions Explained
Actual/365
Standard for many savings and lending products. Divides annual rate by 365 days.
Actual/360
Common in some money-market contexts. Produces slightly higher accrual for the same annual nominal rate.
Actual/366
Used in leap-year precision contexts where day-level accuracy is required.
30/360
Bond-style convention that normalizes each month to 30 days for simplified accrual math.
Sources & References
- Federal Deposit Insurance Corporation (FDIC) - Consumer Resource Center - Deposit-product education context for savings behavior, account terms, and consumer understanding.
- Federal Reserve - Consumers and Communities - Consumer education context for credit, borrowing costs, and financial decision literacy.
- U.S. SEC - Investor.gov - Investor education context for rate comparison, compounding concepts, and risk-aware planning.
- U.S. Department of the Treasury - Federal finance-policy and market-information context relevant to interest-rate and fixed-income background assumptions.