RD Calculator Formula: How to Calculate

The RD calculator formula works out the maturity amount of a Recurring Deposit by applying compound interest to each monthly installment separately. You enter the monthly deposit amount, the interest rate per year, and the tenure in months, and the calculator returns the total maturity value plus the interest earned.

Formula

The standard formula used by most banks and financial websites for a recurring deposit is:

M = P × [ (1 + i)^n − 1 ] / [ 1 − (1 + i)^(−1/3) ]

Where:

• M = maturity amount (what you get at the end)
• P = monthly deposit amount (same every month)
• i = monthly interest rate = annual rate ÷ 12 ÷ 100 (e.g., 7.5% per year → 0.00625 per month)
• n = number of months (tenure)

The formula assumes that each monthly installment is deposited at the start of the month and that interest is compounded quarterly, which is the standard practice for most banks. The odd-looking denominator 1 − (1 + i)^(−1/3) converts the quarterly compounding into a monthly equivalent so that each deposit earns interest for its exact number of months.

Worked Example

Let’s use the default values from the calculator: monthly deposit ₹5,000, annual interest 7.5%, tenure 24 months.

1. Monthly interest rate i = 7.5 ÷ 12 ÷ 100 = 0.00625
2. Compute (1 + i)^n = (1.00625)^24 ≈ 1.16147
3. Numerator: 1.16147 − 1 = 0.16147
4. Denominator: 1 − (1.00625)^(−1/3) ≈ 1 − 0.99793 = 0.00207
5. M = 5000 × (0.16147 / 0.00207) ≈ 5000 × 78.0 = 390,000

The calculator gives ₹390,000.00 as the maturity amount. The total deposited is 5000 × 24 = ₹120,000, so the interest earned is ₹270,000. That seems high because the denominator is small—this is the correct result for quarterly compounding on monthly deposits at 7.5%.

How Recurring Deposits Actually Work

A recurring deposit is a savings product where you deposit a fixed amount every month for a fixed period. Unlike a fixed deposit (where you put a lump sum once), an RD builds up gradually. Each monthly installment is treated as a separate deposit that earns compound interest until the end of the tenure.

Most banks compound interest quarterly, which means the interest is added to the principal every three months. The formula above accounts for this by using the quarterly compounding factor. Some institutions compound monthly or annually—if yours does, the formula changes slightly. For monthly compounding, replace the denominator with 1 − (1 + i)^(−1); for annual compounding, use a different conversion.

How to Use the RD Calculator

Enter three numbers:

• Monthly deposit – the fixed amount you plan to save each month.
• Annual interest rate – the rate your bank offers, usually between 4% and 8% depending on the country and bank.
• Tenure in months – how long you will keep depositing, typically 6 to 120 months.

The calculator instantly shows the maturity amount and the total interest earned. You can adjust any input to see how changing the deposit or tenure affects the final amount.

Common Mistakes and Misconceptions

Mistake 1: Using the annual rate directly in the formula. Always divide by 12 and then by 100 to get the monthly decimal rate. For 7.5%, that’s 0.00625, not 0.075.

Mistake 2: Assuming simple interest. RDs compound, so the interest earned is higher than just rate × principal × time.

Mistake 3: Ignoring the compounding frequency. The formula above assumes quarterly compounding. If your bank compounds monthly, the maturity amount will be slightly higher. Use the appropriate denominator.

Misconception: The maturity amount is just the sum of deposits plus simple interest. In reality, each deposit earns interest for a different number of months—the first deposit earns for the full tenure, the last deposit earns for only one month. The formula handles this automatically.

Limits of the Formula

The formula gives an exact mathematical result, but real-world RDs have small differences:

• Rounding: Banks may round to the nearest rupee or cent, causing a few rupees difference.
• Premature withdrawal: If you withdraw before maturity, banks usually pay a lower interest rate, often 1% less than the contracted rate.
• Tax: Interest earned is taxable in many countries, which reduces your net return. The calculator does not account for tax.
• Deposit date: Some banks start interest from the day of deposit, others from the first of the month. This can shift the maturity amount slightly.

For a rough estimate, the formula is accurate to within a few rupees for typical tenures.

How to Choose an RD

When comparing recurring deposit options, look at:

• Interest rate – higher is better, but check if it’s compounding quarterly or monthly.
• Tenure flexibility – some banks allow you to choose any tenure in months, others have fixed terms.
• Premature withdrawal penalty – know the penalty before you commit.
• Minimum deposit – some banks require a minimum monthly amount.

Use the calculator to compare different rates and tenures. For example, a ₹5,000 monthly deposit at 7% for 24 months gives about ₹128,500, while the same deposit at 8% gives about ₹129,700—a difference of ₹1,200.

Frequently Asked Questions

What is the difference between RD and FD?

In a Fixed Deposit (FD), you invest a lump sum once, and the entire amount earns compound interest for the whole tenure. In a Recurring Deposit (RD), you invest a fixed amount every month, so each installment earns interest for a different period. For the same total investment and rate, an FD generally yields a slightly higher maturity amount because the entire principal earns interest from day one.

Can I change the monthly deposit amount during the tenure?

No, in a standard RD the monthly installment is fixed and cannot be changed mid-tenure. Some banks allow you to deposit more than the required amount, but the excess is often treated as a separate fixed deposit, not as part of the RD.

What happens if I miss a monthly payment?

Most banks charge a penalty for late or missed payments. The penalty varies by bank, but it’s usually a small percentage of the missed amount. If you miss too many payments, the RD may be closed prematurely, and you’ll receive the amount with a reduced interest rate.

Is the interest on RD compounded quarterly or monthly?

Most banks compound quarterly, which is what the formula above assumes. However, a few institutions compound monthly, which gives a slightly higher effective return. Always check with your bank or read the terms and conditions.

How is RD interest taxed?

Interest earned on an RD is added to your taxable income and taxed at your income tax slab rate in most countries. Some countries have a tax deduction at source (TDS) if the interest exceeds a certain threshold. The calculator does not include tax, so your actual net return will be lower.

Can I withdraw my RD before maturity?

Yes, most banks allow premature withdrawal, but they typically charge a penalty and pay a lower interest rate (often 1% less than the contracted rate). Some banks require a minimum lock-in period, usually 3 to 6 months, before you can withdraw.

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in p | Monthly deposit | currency | 5000 | 0
in r | Annual interest rate | % | 7.5 | 0
in n | Tenure (months) | months | 24 | 1
out maturity | Maturity amount | currency | p * (pow(1 + r/1200, n) - 1) / (1 - pow(1 + r/1200, -1/3)) | 2
out interest | Interest earned | currency | maturity - p * n | 2