Savings Goal & Sinking Fund Planner

Enter every goal you're saving for (emergency fund, vacation, a property-tax sinking fund) and see the exact monthly amount each one needs, with interest doing part of the work.

Date: 2026-08-05 Type: App Theme: Saving Status: Idea

What it is

A single-page browser app that takes a list of savings goals (name, target amount, current balance, target date, and the account's APY) and computes the level monthly contribution each one needs to hit its target on time. It runs the math twice per goal: once assuming the balance earns the entered interest rate, once assuming it earns nothing, so the value of parking the money in a better account is visible as a dollar figure instead of a vague "interest helps."

Who it serves

Someone juggling more than one savings target at once: an emergency fund, a car down payment, a holiday-gifts sinking fund, maybe a wedding. Most people either lump all of this into one savings account with no per-goal math, or they know roughly what they're saving for but have never worked out the monthly number that actually gets them there by the date they have in mind.

The money problem it addresses

Sinking funds and short-term goals often sit in whatever account already existed, usually a standard savings or checking account, instead of a high-yield savings account (HYSA). The national average savings account rate was 0.38% APY as of July 2026, per the FDIC, while top HYSAs were paying up to 4.21% APY in August 2026 (NerdWallet). On a short-horizon goal that gap barely matters; on a goal 3–4 years out, it adds up to real money the saver would otherwise have to contribute out of their own paycheck. The planner isolates that number.

How it works

1. Enter goals — the app pre-loads ten synthetic example goals covering a mix of an emergency fund, big-purchase goals (car, home down payment, wedding), and short-horizon sinking funds. Rows are editable; users can add or remove goals.
2. Click Calculate — for each goal, the app grows the current balance forward at the entered APY (compounded monthly, using (1 + APY)^(1/12) − 1 so it matches how banks actually state annual percentage yield) and solves for the level monthly contribution that closes the remaining gap by the target date.
3. Review results — four summary cards show the total monthly amount needed across all goals, what that total would be at 0% interest, the monthly amount saved by earning interest instead, and the total interest earned across every goal by its target date. A bar chart ranks goals by monthly amount needed, highest first, so the user knows where to send money first. A table below breaks out months remaining, monthly contribution, total out-of-pocket contribution, interest earned, and current progress for each goal.

What's in this folder

• README.md — this file.
• cover-image.png — cover illustration used as the card in the web app.
• metadata.md — workflow provenance, model, cover prompt, file manifest.
• requirements.md — functional and technical requirements.
• index.html — single-page entry point; loads style.css and script.js; requires only a modern browser.
• style.css — layout, typography, summary cards, table, and chart styling.
• script.js — goal-row management, the compound-interest sinking-fund math, Chart.js rendering.
• sample-data.json — the ten synthetic goals the app pre-loads, in the same shape, with the APY assumptions documented per goal.

How to run / read it

Open index.html in any modern browser. No build step, no server, no API keys, and it works straight from file://. Sample data loads automatically. Click Calculate My Plan to see results immediately, or edit the goal rows first.

Estimated impact

Run against the ten sample goals, the plan needs $3,956.07/month total if every balance earns its entered APY, versus $4,135.65/month if the same money sat at 0%. That's a $179.59/month difference the saver doesn't have to find from their paycheck, just from where the money lives. Across all ten goals, it adds up to $5,163.55 in interest earned by their target dates.

The size of that effect depends entirely on the time horizon. The 48-month home-down-payment goal earns $3,828.31 in interest on its own, most of the total. The three short sinking funds in the sample (4, 5, and 6 months out), left at the 0.38% national-average rate instead of a 4.00% HYSA, would only save a combined $11.24/month by switching accounts, barely worth the effort of opening a new one. Below roughly a year, account choice barely moves the number, and the planner shows that honestly instead of implying every goal benefits equally.

Good to know

This is a planning and organizing tool, not personalized financial or tax advice. It assumes the entered APY holds constant for the full savings period, which real HYSA rates don't; they move with the Fed funds rate and can drop with little notice. It doesn't account for taxes on interest earned, which is taxable income in the U.S. Treat the monthly numbers as a starting plan, not a guarantee, and check your account's current APY before relying on them.

Sources

• https://www.nerdwallet.com/banking/best/high-yield-online-savings-accounts — best HYSA rates, up to 4.21% APY, August 2026
• https://www.forbes.com/advisor/banking/savings/best-high-yield-savings-accounts/ — best HYSA rates, up to 4.00% APY, August 2026
• https://www.fool.com/money/research/average-savings-account-interest-rate/ — average U.S. savings account rate 0.38% APY as of July 2026 (FDIC), average HYSA rate 1.60%, average 1-year CD 2.49%
• https://www.fdic.gov/national-rates-and-rate-caps — FDIC National Rates and Rate Caps, July 2026