Proof of Budget

Goal calculator

Sinking Fund Calculator

A sinking fund is a small pot you fill on purpose, a little at a time, for an expense you can see coming: car repairs, an annual insurance bill, holiday gifts, a vet visit, a trip. Spread the cost across the months before it lands, and a scary bill turns into a quiet monthly line.

Three long envelopes standing in a row, filled to different heights with kraft paper and marked with a calendar
Three pots, three timelines.

What do you want to find out?

Calculator mode

Leave at 0 if your pot earns nothing, or if you would rather plan cautiously. This is your own estimate, not a promise.

    Fine print, in plain words

    How the calculator thinks

    Using it

    1. Pick a mode. "How much each month" needs a target date. "When I will reach the goal" needs a monthly amount you can really afford.
    2. Name the goal, enter the amount you need, and enter what you already have set aside for it.
    3. Read the result card: the monthly amount or finish date, how much you will contribute, and the month you cross 25, 50, 75 and 100 percent.
    4. Press "Send total to the planner" to create or update a Sinking funds envelope with the combined monthly amount.

    What it assumes

    • You contribute once a month, on the same day of the month as today. The first contribution is one month from now.
    • Months are whole months between today's date and your target date.
    • With interest left at zero, the maths is simple division. With a rate entered, interest is added monthly (one twelfth of the yearly rate) before each contribution.
    • Taxes, fees and rising prices are ignored. If a cost tends to creep up, padding the goal a little is a kind thing to do for your future self.
    • Every number comes from you, or from the clearly labelled illustrative example.

    Edge cases

    • Date in this month or the past: there is no month left to spread it across, so the card shows the whole remaining amount as one payment.
    • Already saved enough: the card says so and asks for nothing.
    • Blank or negative boxes: flagged on the card, and left out of the total.
    • Very long timelines: anything past one hundred years is reported as "more than 100 years" instead of a date.

    Ideas for sinking fund envelopes

    • Car maintenance and repairs
    • Insurance billed once or twice a year
    • Gifts and holidays
    • Medical, dental and eye care
    • Home repairs
    • Pet care
    • Back to school
    • Travel and visiting family
    • Yearly renewals and subscriptions
    • Replacing a phone or laptop

    A sinking fund is for expenses you expect. An emergency fund is for the ones you do not. They can sit side by side as separate envelopes. This tool is a planning aid, not financial advice.