Finance
Daily Compound Interest Calculator
Estimate daily compound growth over years, months, and days, including reinvested interest, weekday filters, and optional cash flows.
Inputs
Results
Useful next checks
- Compare a few scenarios before making a decision.
- Check rates, fees, tax, and timing outside the estimate.
- Use the explanation below to understand the formula.
Intro
Use this daily compound interest calculator to model investments, trading balances, or savings scenarios where interest or earnings are added day by day. It is designed for short or long daily projections where the exact active days, reinvestment rate, and cash flows matter.
The result shows the final balance, total interest earned, how much interest was reinvested, any interest taken out as cash, deposits, withdrawals, active compounding days, and a period breakdown.
What you can calculate
This calculator supports daily compounding scenarios such as:
- How much a starting balance could become after a set number of days, months, and years.
- The difference between daily, weekly, monthly, and yearly quoted rates.
- How excluding weekends or choosing custom compounding days changes the result.
- What happens when you reinvest only part of the daily interest.
- How recurring deposits or withdrawals affect a daily compounding plan.
- The daily workings behind the result, using the CSV export.
For a broader savings projection with monthly, quarterly, yearly, or custom compounding periods, use the Compound Interest Calculator.
Inputs explained
| Input | What it means |
|---|---|
| Principal amount | The starting balance before any one-time additional deposit. |
| Interest rate | The percentage rate for the selected rate period. |
| Rate period | Whether the entered rate is daily, weekly, monthly, or yearly. |
| Daily reinvest rate | The percentage of positive daily interest kept in the balance for future compounding. |
| Years, months, and days | The calendar length of the projection. |
| Start date | The date used to determine weekdays and scheduled cash flows. If blank, today is used. |
| Days to include | Whether interest compounds every day, weekdays only, or on a custom set of weekdays. |
| Additional deposits | Optional recurring deposits plus an upfront one-time deposit. |
| Additional withdrawals | Optional recurring withdrawals, capped at the available balance. |
How the calculation works
The calculator first converts the entered rate into a daily rate. A daily rate is used directly. Weekly, monthly, and yearly rates are divided by 7, by 365/12, or by 365 respectively.
For each calendar day in the projection, the calculator checks whether that weekday is active. On active days it calculates:
Daily interest = balance × daily rate
If the interest is positive, the reinvest rate determines how much is added back to the balance. For example, an 80% reinvest rate adds 80% of that day’s interest to the balance and treats the remaining 20% as interest withdrawn.
Deposits and withdrawals are applied at the end of their scheduled day, after any interest for that day. One-time additional deposits are added at the start of the projection.
Example calculation
Suppose you start with 1,000 and earn 0.4% per day for 365 days with all interest reinvested.
The daily formula is:
A = P × (1 + r)^t
Where P is 1,000, r is 0.004, and t is 365. The estimated final balance is about 4,293.44 before any fees, taxes, or variable returns.
If you change the reinvest rate to 80%, only 80% of each positive day’s interest stays in the balance. The balance grows more slowly, and the remaining interest is shown separately as withdrawn interest.
Active days and start dates
The term is treated as a calendar span. If you enter one year from a start date, the end date is one calendar year later. Choosing weekdays only does not shorten the calendar span; it simply skips interest calculations on Saturdays and Sundays.
Custom days are useful for trading or investment assumptions where earnings only occur on certain days. Deposits and withdrawals still follow their own schedule, even on days when interest is not compounded.
Assumptions and limitations
- The entered rate is assumed to stay constant for the whole projection.
- Monthly rates are converted using 365/12 days.
- Deposits and withdrawals are applied at the end of scheduled days.
- Withdrawals are capped at the available projected balance.
- Fees, taxes, inflation, spreads, platform charges, and changing market returns are not included.
- Results are educational estimates, not financial advice or return guarantees.
FAQs
- What is daily compounding? Daily compounding means interest is calculated and added to the balance each active day, allowing future interest to be earned on earlier interest.
- Can I exclude weekends? Yes. Choose weekdays only, or choose a custom set of days.
- What is the daily reinvest rate? It is the share of positive daily interest kept in the balance. A lower reinvest rate models taking some interest out as cash.
- Can the calculator handle withdrawals? Yes. Choose withdrawals, enter an amount and frequency, and the calculator caps withdrawals at the available balance.
- Why does the start date matter? The start date determines which calendar dates are weekdays and when weekly, bi-weekly, or monthly cash flows happen.
Frequently asked questions
What is daily compound interest?
Daily compound interest adds interest to the balance each active day, so later days can earn interest on earlier interest.
What does the reinvest rate do?
It controls how much of each day’s positive interest is kept in the balance. The remainder is shown as interest withdrawn.
Can I exclude weekends?
Yes. Choose weekdays only, or choose custom days to include any mix of weekdays.
When are deposits and withdrawals applied?
Recurring deposits and withdrawals are applied at the end of their scheduled day, after any daily interest calculation.