RD Calculator Excel Sheet: The Quarterly Compounding Formula, Cell by Cell, With a Year-by-Year Table

An RD maturity is not deposit × rate × years. Each monthly instalment earns interest for a different length of time, and the interest is compounded every quarter. That is why a simple interest formula in Excel gives the wrong answer. This post shows the formula that post office and bank RDs use, cell by cell, and checks it against the maturity table in the post office scheme rules. Then it works two cases, ₹5,000 and ₹7,000 a month for 5 years, with the balance at the end of every year.

The rate in the sheet: 6.7% for October–December 2026

The National Savings Institute (NSI) lists the 5-year National Savings Recurring Deposit at 6.7% from 1 October 2023 to 30 September 2026. On 30 September 2026 the Department of Economic Affairs said the small savings rates for 1 October to 31 December 2026 stay unchanged from the July–September quarter. So the post office RD rate for this quarter is still 6.7%. The rate is reviewed every quarter, so check it again before you rely on a 5-year figure.

Source: National Savings Institute: National Savings Recurring Deposit Account, interest rate history (6.7% from 1.10.2023 to 30.09.2026)

Source: Department of Economic Affairs OM F.No. 1/4/2019-NS, 30 Sep 2026: small savings rates for 1 Oct to 31 Dec 2026 unchanged from Q2 (enclosed with Department of Posts SB Order No. 12/2026)

What's in the RD tab

The formula, and why it has a −1/3 in it

The −1/3 is there because a month is one third of a quarter. Each deposit grows by (1 + i) for every full quarter it stays in the account, and by (1 + i)^(1/3) for each month. The first deposit stays 60 months, the last one stays 1 month. The formula adds all 60 of them in one step, so you do not need a 60-row table to get the maturity.

Checked against the post office's own table

The National Savings Recurring Deposit Scheme, 2019 prints the maturity value for a ₹100 a month account in Table 1.1 of paragraph 9(1). For accounts opened from 12 December 2019 to 31 March 2020 it is ₹7,231.38, and for accounts opened on or after 1 April 2020 it is ₹6,969.67. NSI's rate history shows 7.2% and 5.8% for those two periods. Put ₹100 and 7.2% into the formula and it gives ₹7,231.38. Put in 5.8% and it gives ₹6,969.67. Both match to the paisa, so the sheet follows the post office method. Paragraph 9(1) also says other deposit amounts get proportionate values, so a ₹5,000 account gets 50 times the ₹100 figure.

Source: NSI: National Savings Recurring Deposit Scheme, 2019 (G.S.R. 918(E), 12 Dec 2019, as amended by G.S.R. 285(E), 5 May 2020), paragraph 9(1) and Table 1.1

Worked example: ₹5,000 a month for 5 years at 6.7%

• Quarterly rate i: 6.7 ÷ 400 = 0.01675
• Quarters q: 5 × 4 = 20
• (1.01675)^20 = 1.394067, so the top of the formula is 0.394067
• (1.01675)^(−1/3) = 0.994478, so the bottom is 1 − 0.994478 = 0.005522
• 0.394067 ÷ 0.005522 = 71.3658. Every ₹1 a month grows to about ₹71.37 (or ₹7,136.58 for ₹100 a month)
• Maturity: ₹5,000 × 71.3658 = ₹3,56,829
• Deposited: ₹5,000 × 60 = ₹3,00,000. Interest: ₹56,829

Worked example: ₹7,000 a month for 5 years at 6.7%

• Same factor, 71.3658, because the rate and the term are the same
• Maturity: ₹7,000 × 71.3658 = ₹4,99,561
• Deposited: ₹7,000 × 60 = ₹4,20,000. Interest: ₹79,561
• In the sheet: type 7000 in B5. B12 shows the maturity and B13 the interest.

Add a year-by-year table

The RD tab gives the maturity only. To see the balance at the end of each year, add a small table under it. Type the headings in row 21, put the years 1 to 5 in A22 to A26, then fill these formulas down from row 22. The balance at the end of year y is the same formula with y in place of the full term, because the deposits made so far have each been compounded up to that date.

Look at the last column. More than a third of the 5-year interest comes in the fifth year, because by then the account holds four years of deposits that are all earning. That is also why breaking an RD early costs more than it seems.

TDS on RD interest

Under the Income-tax Act, 2025, a bank, a co-operative bank, or a post office (for deposits under a notified scheme) deducts TDS on interest once the interest it credits or pays you in a tax year goes above a threshold. The threshold is ₹50,000 for most people and ₹1,00,000 for a senior citizen (section 393(1), Table, Sl. No. 5(ii)). Once the total crosses it, TDS applies to the entire amount, not just the part above it. The Income Tax Department's TDS rates page gives the rate for residents as 10%.

Source: Income-tax Act, 2025, section 393(1), Table, Sl. No. 5(ii) and Note 1 (incometaxindia.gov.in)

Source: Income Tax Department: TDS rates, section 393(1) [Table S. No. 5(ii) & (iii)], interest other than interest on securities, 10%

• A single ₹7,000 a month RD earns at most ₹29,610 in its best year in the table above, which is below ₹50,000 on its own.
• The threshold counts all the interest the same bank credits to you in the tax year, so an FD with the same bank can push you over it.
• Our table counts years from the month the RD opens, not April to March, so treat it as a guide to which years come close.
• TDS is not the final tax. RD interest is part of your income and is taxed at your slab rate. The sheet's B14 works out that tax from the slab you type in B8.
• Section 393(6) lets a resident individual give the payer a written declaration, in the prescribed form, that the tax on their estimated total income for the year will be nil. Then the bank does not deduct TDS. The same sub-section limits this for people under 60, so check with your bank whether you qualify.

What the sheet does not count

The formula assumes all 60 instalments are paid on time. The post office scheme rules add a few things that change the real figure:

• Missed instalments: with up to four defaults you can extend the maturity by the same number of months. More than four and the account is treated as discontinued; it can be revived within two months of the fourth default by paying the missed deposits with a fee of ₹1 per ₹100 for each month of default (paragraph 6).
• Advance deposits: paying six to eleven months ahead earns a rebate of ₹10 on a ₹100 account, and twelve months ahead earns ₹40, proportionately for other amounts (paragraph 7).
• Premature closure: allowed after three years, with interest at the Post Office Savings Account rate, not the RD rate (paragraph 8).
• Loan: up to 50% of the deposits after one year and twelve deposits (paragraph 14).

Bank RDs follow the same quarterly formula, but each bank sets its own rate, penalty and premature closure rules. Change B6 to your bank's rate and check its rules before you open the account. These are estimates for information, not advice.