# Savings Goal Calculator - Monthly Deposit Needed or Time to Reach a Target

Page: https://hirantha.me/tools/savings-goal-calculator
Part of: Hirantha Sandaruwan Lakshan free tools (https://hirantha.me/tools)
Updated: 2026-10-13

The monthly deposit needed to reach a target by a date at a given interest rate, or how many months a deposit takes.

This is a free tool that runs in the browser: open the page to use it. File tools process files on the visitor's own device; files are never uploaded or stored. No account, sign-up, payment or watermark.

Type your goal, what you have saved so far and an interest rate. Then either give a time and get the monthly deposit you need, or give a monthly deposit and get the months it takes. It uses monthly compounding and end-of-month deposits, and handles a rate of 0%. Everything runs in your browser.

Each month the balance earns one twelfth of the yearly rate, then you add your deposit at the end of the month. With a monthly rate i, an existing balance B and a deposit D, the balance after n months is B x (1 + i) to the power n + D x ((1 + i) to the power n - 1) / i. This is the future value of an ordinary annuity.

To find the deposit, set that balance equal to your goal T and solve: D = (T - B x (1 + i) to the power n) x i / ((1 + i) to the power n - 1). At a rate of 0% it is simply (T - B) / n. The answer is rounded up to the next cent so that paying it really does reach the goal. If your existing balance alone grows to the goal in time, the deposit is zero.

To find the time, solve for n: n = ln((T x i + D) / (B x i + D)) / ln(1 + i), then round up to a whole month. The tool also checks the month before, so it never shows one month too many. Choose a target date and the months are counted as whole months from the start date to that date.

The rate is assumed to stay the same, and the last deposit earns no interest because it goes in at the end of the month. If you deposit at the start of the month you need slightly less. Interest is before tax. In Sri Lanka, deposit interest normally has 10% advance income tax deducted unless you gave your bank a self-declaration (we checked the Inland Revenue Department's circular on 13 October 2026; confirm with your bank), so for a rough after-tax figure enter 90% of the rate, for example 7.2% for an 8% account.

Monthly deposit needed to reach Rs. 1,000,000 from nothing (monthly compounding, end-of-month deposits, rounded up to the cent):
| Time | 0% a year | 5% a year | 8% a year | 12% a year |
| --- | --- | --- | --- | --- |
| 1 year | Rs. 83,333.34 | Rs. 81,440.82 | Rs. 80,321.77 | Rs. 78,848.79 |
| 3 years | Rs. 27,777.78 | Rs. 25,804.24 | Rs. 24,669.70 | Rs. 23,214.31 |
| 5 years | Rs. 16,666.67 | Rs. 14,704.57 | Rs. 13,609.73 | Rs. 12,244.45 |
| 10 years | Rs. 8,333.34 | Rs. 6,439.89 | Rs. 5,466.10 | Rs. 4,347.10 |

Q: How much should I save each month to reach my goal?
A: It depends on the goal, the time and the rate. Type them in, or look at the table: for Rs. 1,000,000 in 5 years you need Rs. 16,666.67 a month at 0% and Rs. 12,244.45 a month at 12%. Interest does more of the work the longer you save.

Q: What if the interest rate is zero?
A: Then there is no growth and the monthly deposit is the goal, minus what you have saved, divided by the number of months. Enter 0 in the rate box for a plain savings box at home.

Q: Are the deposits at the start or the end of the month?
A: At the end, the usual convention for this formula. Deposits at the start of each month earn one more month of interest each, so you would need a little less than the figure shown.

Q: Why is the final balance a few cents above my goal?
A: The deposit is rounded up to the next cent so that you reach the goal rather than fall a hair short. The unrounded deposit would reach it exactly. The overshoot is at most one cent on each monthly deposit, grown with interest.

Q: How are the months between two dates counted?
A: As whole months from the start date to the target date: a month counts once the day of the month is reached, or once the target is the last day of a shorter month (31 January to 28 February is one month). From 13 October 2026 to 13 October 2031 is 60 months. One deposit is made at the end of each month.

Q: What if the goal cannot be reached?
A: If the deposit is too small, the tool says the goal would take more than 100 years. If you have no deposit and no growth on your savings, it asks for a deposit. Raise the deposit or lower the goal.

Sources: Annuity (future value of an ordinary annuity) - Wikipedia (https://en.wikipedia.org/wiki/Annuity); Compound interest - Wikipedia (https://en.wikipedia.org/wiki/Compound_interest); Inland Revenue Department circular SEC/2025/E/02: advance income tax on deposit interest (https://www.ird.gov.lk/en/publications/Circulars_Circulars/SEC_2025_E_02_E.pdf)

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