Daily Interest Calculator
Estimate daily interest accrual for savings, loans, or investments
How to Use This Tool
Enter your principal amount (the initial sum of money for savings, loan, or investment) in the first field. Input your annual interest rate as a percentage (e.g., 4.5 for 4.5% annual interest).
Add the number of days you want to calculate interest for, then select whether you are using simple interest or daily compound interest. Choose your day count convention: 365-day for most personal finance uses, or 360-day if your bank uses banker’s year calculations.
Click Calculate Interest to see your results, or Reset to clear all fields. Use the Copy Results button to save your calculation to your clipboard for budgeting or record-keeping.
Formula and Logic
Simple interest calculations use the following formula for daily interest:
- Daily Interest = (Principal × Annual Rate ÷ 100) ÷ Day Count
- Total Interest = Daily Interest × Number of Days
- Total Balance = Principal + Total Interest
Compound interest (daily compounding) uses exponential growth to calculate balance:
- Daily Rate = (Annual Rate ÷ 100) ÷ Day Count
- Total Balance = Principal × (1 + Daily Rate) ^ Number of Days
- Total Interest = Total Balance - Principal
- Effective Annual Rate (EAR) = [(1 + Daily Rate) ^ Day Count - 1] × 100
Day count convention adjusts the daily rate: 365-day divides by 365 (actual days in a year), 360-day divides by 360 (common for commercial banking and loans).
Practical Notes
Interest rates on savings accounts and loans are almost always quoted as annual percentage rates (APR). This tool converts that annual rate to a daily rate for accurate accrual calculations.
Daily compounding will always yield higher returns (or higher interest owed) than simple interest over the same period, as interest is added to the principal each day and earns additional interest.
Interest earned on savings is often taxable as ordinary income in most jurisdictions. This tool does not account for taxes, so subtract your marginal tax rate from total interest earned to estimate after-tax returns.
Some loans use 360-day years to calculate daily interest, which results in slightly higher interest charges than a 365-day year. Check your loan agreement to confirm which convention your lender uses.
For budgeting, daily interest calculations help you track how much interest you are accruing on credit card debt or high-yield savings each day, making it easier to adjust spending or savings habits.
Why This Tool Is Useful
Most basic interest calculators only show monthly or annual results, but daily interest accrual is critical for short-term loans, credit card balances, and high-yield savings accounts that compound daily.
Individuals managing credit card debt can use this tool to see how much interest accrues each day, helping them prioritize extra payments to reduce principal faster.
Savers can compare daily compounding rates across high-yield savings accounts to see how small differences in annual rates impact daily earnings over time.
Financial planners use daily interest calculations to model short-term cash flow for clients, especially for bridge loans, short-term investments, or temporary savings goals.
Frequently Asked Questions
Does this calculator account for taxes on interest earned?
No, this tool calculates gross interest before taxes. You will need to subtract your marginal income tax rate from the total interest earned to estimate your after-tax returns, as most interest income is taxable.
Why do some banks use a 360-day year instead of 365?
The 360-day year (banker’s year) simplifies interest calculations for commercial loans and dates back to when manual calculations were more common. It results in a slightly higher daily interest rate, which increases total interest owed for loans and reduces interest earned for savings compared to a 365-day year.
How does daily compounding differ from simple daily interest for long periods?
Simple daily interest calculates interest only on the original principal each day, while daily compounding adds interest to the principal each day, so subsequent interest is calculated on the growing balance. Over long periods (e.g., 1+ years), compounding can result in significantly higher total interest for savings, or higher total owed for loans.
Additional Guidance
Always verify the interest rate type and day count convention with your bank or lender before using calculations for official financial planning. Rates may be variable, so recalculate if your annual rate changes.
For credit card debt, most issuers use daily compounding and a 365-day year. Use this tool to see how much interest you accrue each day, then aim to pay more than the daily interest amount to reduce your principal balance.
If you are calculating interest for a leap year, the 365-day convention will use 366 days for the full year, but this tool uses the day count you input, so adjust the number of days manually if calculating across a leap year.