Sinking Fund Calculator

Growth Graph

This chart plots balance by period using your generated schedule.

Calculator Inputs

Choose what you want to solve, set a rate and frequency, then submit to generate a full schedule.

Calculation mode

Switch between “deposit” and “future value” workflows.

Target future amount

Amount you want at the end of the plan.

Periodic deposit (for Future Value mode)

Leave as-is when solving deposits automatically.

Time horizon (years)

The plan length in years.

Initial deposit

Starting balance added before the first period.

Annual interest rate (%)

Nominal annual rate, before compounding conversion.

Compounding

Used to derive the effective annual rate.

Deposit frequency

Sets the number of periods and schedule length.

Deposit timing

Beginning deposits earn interest for the full period.

Inflation rate (%)

Optional: to express the target in today’s money.

Treat target as today’s value (inflate forward)

Target used = target × (1+inflation)^years.

Tax on interest (%)

Optional: reduces each period’s credited interest.

Example Data Table

Use these sample inputs to test the calculator quickly.

Target	Years	Annual Rate	Compounding	Deposit Frequency	Timing	Initial
10,000	5	6%	Monthly	Monthly	End	0
50,000	8	7.5%	Quarterly	Monthly	Begin	2,500

Formula Used

This tool models a sinking fund as an initial deposit plus a constant periodic deposit that grows with a periodic effective rate.

Convert nominal annual rate to an effective annual rate: (1 + r/m)^m − 1 (or e^r − 1 for continuous).
Convert effective annual to contribution-period rate: i = (1 + r_eff)^(1/k) − 1.
Future value (ordinary): FV = P0(1+i)^n + PMT * ((1+i)^n − 1)/i.
Future value (due): multiply the series term by (1+i).
To solve deposits, rearrange to: PMT = (FV − P0(1+i)^n) / A, where A is the series factor (ordinary or due).

How to Use This Calculator

Select the calculation mode: solve deposits or solve future value.
Enter your target amount, time horizon, and annual rate.
Choose compounding and deposit frequency, then pick deposit timing.
Optionally add inflation (to treat the target as today’s money) and tax on interest.
Click Submit to view the summary and full schedule above the form.
Use the export buttons to download CSV or PDF for reporting.

Deposit Frequency And Period Count

A monthly plan uses 12 periods per year, while weekly uses 52. Over 5 years, that becomes 60 versus 260 deposits. More periods can smooth cash flow, but the calculator keeps math consistent by converting the effective annual rate into a matching periodic rate.

Compounding Choice And Effective Rate

If the nominal annual rate is 6% and compounding is monthly, the effective annual rate becomes about 6.168%. With quarterly compounding, it is about 6.136%. The calculator shows this value so you can compare products using the same yardstick.

Timing Impact Ordinary Vs Due

Deposits at the beginning of each period earn one extra period of growth. With a 0.5% periodic rate and 60 periods, the due schedule multiplies the series factor by (1+i), typically reducing the required deposit by about 0.5%–1.0%, depending on the horizon.

Inflation As A Target Converter

If your target is 10,000 in today’s money, 6% inflation over 5 years implies a nominal target near 13,382. Enabling inflation makes the calculator solve for the bigger future number while keeping your input meaning “today’s value.”

Tax On Interest And Net Growth

When tax on interest is 15%, each period’s earned interest is reduced to 85% before being credited. Over long horizons, this can materially change the ending balance even if deposits stay the same, because compounding is applied to the net interest stream.

Scenario Comparison Using Exports

Exported CSV and PDF include inputs, summary metrics, and the full schedule table. Use them to compare “rate-up” versus “time-up” strategies. For example, raising the annual rate from 6% to 7% often lowers the required deposit more than trimming 6 months from the horizon increases it.

Frequently Asked Questions

1) What is a sinking fund in simple terms?

A sinking fund is a planned savings pool where you deposit regularly to reach a specific future expense, like tuition, repairs, or a replacement purchase.

2) Why does compounding matter if I deposit monthly?

Compounding changes the effective annual growth. This calculator converts the chosen compounding rule into a matching periodic rate, so monthly deposits align with the actual growth assumption.

3) Should I choose beginning or end of period deposits?

Beginning-of-period deposits generally require slightly less per period because each deposit earns interest for a longer time. Choose the option that matches how you actually deposit.

4) What does “tax on interest” represent here?

It models interest being taxed each period, reducing credited interest. It is a planning approximation and may differ from real tax rules, which can be annual or transaction-based.

5) How is inflation applied to the target?

If enabled, the target you enter is treated as today’s value and is inflated forward using (1+inflation)^years, producing a higher nominal target to fund in the future.

6) Why can my final value miss the target in Future Value mode?

Future Value mode calculates what your chosen deposit produces. If it is below the target, increase deposits, extend years, or revise the expected rate assumptions to close the gap.