Monthly deposits, maturity, and interest earned
Maturity combines all monthly deposits with estimated interest. Early installments earn for longer than later ones. The effective annual yield describes the quoted rate with quarterly reinvestment; it is not interest divided by the total deposits. The table includes a final partial year at its actual installment month. Required deposits are rounded for display while the projection keeps the unrounded installment.
If the entire amount is available on the opening date, compare a single deposit using the Fixed Deposit Calculator instead of treating it as monthly installments.
The formula
The annual rate is a decimal and n is the number of monthly installments. The calculation advances one equal month at a time using the cube root of the quarterly factor. At zero interest, maturity is simply the installment multiplied by the number of months. Month entry supports 1–240 installments. Reverse solving divides the target by the same installment growth stream, so both modes use the same rate and timing.
An installment timing check
If you deposit 1,000 each month for two years at zero interest, the balance is 24,000. With a positive rate, start-of-month deposits earn one extra month of interest compared with otherwise identical end-of-month deposits.
How to use this calculator
- Choose maturity from a monthly installment, or the installment needed for a target maturity.
- Enter a fixed quoted annual rate and a term in whole years or whole months.
- Choose start or end of each month, then compare deposits, gross interest and the final balance.
Quarterly compounding with monthly installments
A recurring deposit has monthly cash flows even when the quoted interest compounds quarterly. Applying a simple annual rate to the total deposits overstates interest because most of that money was not present on the opening date. Each installment needs its own remaining earning period.
This model converts quarterly growth into equal monthly factors. Banks may instead use actual payment dates and actual-day calculations, including leap years and broken periods. Missed installments, delayed payments, penalties, and premature closure can therefore change the amount finally paid.
Plan a target deposit amount
Choose Required monthly deposit when you know the amount needed at maturity. A term of 18 months can be entered directly. At zero interest, a 90,000 target over 18 months needs 5,000 per installment.
A bank may require particular installment multiples or offer a narrower term range. The mathematical result does not establish eligibility. Round to an allowed amount and use maturity mode to check that installment.
Assumptions & limitations
What this calculation assumes
- The installment and quoted rate stay fixed.
- Every deposit is made on time.
- A year contains twelve equal modeled months.
What to keep in mind
- This is not an exact bank maturity quote.
- No tax, withholding, late fees, or withdrawal penalties are deducted.
Common questions
Why is this different from the SIP calculator?
The RD estimate converts a quarterly-compounded deposit rate to a monthly factor. The SIP model divides a nominal annual return directly by twelve. Their rate conventions are different.
Can I model an irregular deposit schedule?
No. Use this result only for equal monthly installments. Actual irregular payments require a dated cash-flow calculation.
Can I enter a term shorter than a year?
Yes. Choose Months and enter 1–240 whole months. This is a calculation range, not a bank product’s permitted term.
Does required deposit guarantee the target?
It reaches the target within this fixed-rate model using an unrounded installment. Bank payment dates, allowed installment amounts, deductions and penalties can change the actual maturity.
Sources & further reading
Reviewed on