This tool estimates growth using a 365-day year. Real accounts may vary by institution and product terms.
Why a daily interest calculator matters
A daily interest calculator helps you estimate how much money you earn (or owe) over a specific number of days. It is useful for savings accounts, money market balances, short-term investments, and even understanding loan or credit card costs.
Most people think in months or years, but interest often accrues daily. That means your money can change every single day, and small differences in rate or timing can add up quickly.
How this calculator works
1) Daily compounding
In this mode, each day’s interest gets added to the balance, and the next day earns interest on a slightly larger amount.
A = P × (1 + r/365)d
- A = ending balance
- P = starting balance
- r = annual rate in decimal form (for 5%, use 0.05)
- d = number of days
2) Simple interest (no compounding)
In simple interest mode, interest is earned only on the original principal.
A = P × (1 + r × d/365)
When to use each method
- Use daily compounding for high-yield savings accounts, many brokerage cash products, and compounding investment estimates.
- Use simple interest for rough estimates, certain short-term contracts, or products that do not compound daily.
Quick example
Suppose you deposit $10,000 at 5% annual interest for 60 days.
- Simple interest gives a straightforward estimate based on principal only.
- Daily compounding gives a slightly higher result because interest starts earning interest.
Over short periods the difference may look small, but over longer periods it becomes much more noticeable.
APR vs APY: what you should know
APR is the annual rate before considering compounding. APY includes the effect of compounding. If an account compounds daily, APY will generally be higher than APR for the same stated rate.
If you are comparing banks or financial products, always compare like-for-like values and check whether rates are promotional, variable, or tiered.
Common mistakes to avoid
- Entering monthly rate as annual rate (or vice versa).
- Using 30 days for every month when your product accrues interest daily.
- Ignoring account fees that may offset earned interest.
- Assuming all institutions use the same day-count convention.
Practical uses for this tool
Short-term savings goals
Estimate how much your emergency fund can grow in 30, 60, or 90 days.
Cash management decisions
Compare two accounts with different rates to see where your cash should sit.
Debt awareness
While this page focuses on earnings, the same daily-interest concept can help you understand how debt grows if unpaid.
Final thought
Daily interest may look tiny on any single day, but consistency compounds over time. Use this calculator to make smarter financial decisions, compare options, and build a habit of checking the real cost or benefit of where your money lives.