{ "slug": "sinking-fund-monthly", "title": "Sinking Fund Monthly Contribution Calculator", "heading": "Sinking Fund Calculator", "category": "financial", "url": "https://www.revenuelab.fyi/toolbox/sinking-fund-monthly", "summary": "Work out the monthly set-aside for a known future expense so it never hits credit.", "description": "A sinking fund is a savings account with a job: a known expense at a known date, funded in advance in equal instalments. Property tax bills, insurance renewals, a car replacement, a roof, a wedding — all of them are predictable, and all of them end up on a credit card when they are not pre-funded. This calculator takes the target amount, the date it is due, what you have already saved, and the interest your savings earn, and returns the exact monthly contribution required. Fund the largest, nearest item first; a fund that is short at the deadline still cost you the discipline without the benefit.", "formula": "With interest: contribution = (Target − Current×(1+r)^n) × r ÷ ((1+r)^n − 1), where r is the monthly rate and n is months remaining. With no interest: (Target − Current) ÷ n.", "dateModified": "2026-08-25", "run_url": "https://www.revenuelab.fyi/api/public/calc?tool=sinking-fund-monthly", "inputs": [ { "id": "target", "label": "Amount you'll need", "kind": "number", "hint": null, "default": 6000, "unit": "$", "min": 1, "max": null }, { "id": "months", "label": "Months until it's due", "kind": "number", "hint": null, "default": 18, "unit": "months", "min": 1, "max": null }, { "id": "current", "label": "Already saved", "kind": "number", "hint": null, "default": 800, "unit": "$", "min": 0, "max": null }, { "id": "apy", "label": "Savings APY", "kind": "number", "hint": null, "default": 4, "unit": "%", "min": 0, "max": null }, { "id": "inflation", "label": "Annual cost inflation on the item", "kind": "number", "hint": null, "default": 3, "unit": "%", "min": 0, "max": null } ], "outputs": [ { "id": "contribution", "label": "Monthly contribution needed", "format": "currency", "hint": null, "primary": true }, { "id": "weekly", "label": "Equivalent weekly amount", "format": "currency", "hint": null, "primary": false }, { "id": "inflated", "label": "Cost at the due date", "format": "currency", "hint": null, "primary": false }, { "id": "gap", "label": "Gap left to fund", "format": "currency", "hint": null, "primary": false }, { "id": "contributed", "label": "Total you'll contribute", "format": "currency", "hint": null, "primary": false }, { "id": "interestEarned", "label": "Interest doing the rest", "format": "currency", "hint": null, "primary": false } ], "worked_example": { "inputs": [ "Amount you'll need: 6000 $", "Months until it's due: 18 months", "Already saved: 800 $", "Savings APY: 4 %", "Annual cost inflation on the item: 3 %" ], "outputs": [ "Monthly contribution needed: $292.81", "Equivalent weekly amount: $67.57", "Cost at the due date: $6,272.01", "Gap left to fund: $5,422.63", "Total you'll contribute: $5,270.61", "Interest doing the rest: $201.41" ] }, "how_to": { "title": "How to use this", "steps": [ "Enter amount you'll need ($).", "Enter months until it's due (months).", "Enter already saved ($).", "Enter savings apy (%).", "Enter annual cost inflation on the item (%).", "Read your monthly contribution needed on the right — it updates as you type.", "Hit Share to keep the scenario or send it to someone." ] }, "scenarios": [ { "name": "Conservative", "description": "Lower-end numbers — what if things land soft?", "values": { "target": 3600, "months": 11, "current": 500, "apy": 2.4, "inflation": 1.7999999999999998 } }, { "name": "Typical", "description": "Defaults — the most common real-world setup.", "values": { "target": 6000, "months": 18, "current": 800, "apy": 4, "inflation": 3 } }, { "name": "Ambitious", "description": "Higher-end numbers — what if things really pop?", "values": { "target": 9600, "months": 29, "current": 1300, "apy": 6.4, "inflation": 4.800000000000001 } } ], "limitations": [ "Results are estimates before tax, fees, and inflation unless an input explicitly covers them.", "Rates are treated as fixed for the whole period — variable-rate products will drift from this projection.", "This is educational maths, not financial advice. Check anything contractual with the lender or your accountant." ], "faq": [ { "q": "How is this different from an emergency fund?", "a": "An emergency fund covers unknown events and should not be spent on scheduled ones. A sinking fund covers a known expense with a date. Keeping them in separate accounts is what stops a predictable car registration bill from quietly draining the buffer meant for job loss." }, { "q": "Where should the money sit?", "a": "Somewhere liquid and insured — a high-yield savings account or money market fund. For horizons beyond a couple of years, a short-dated CD or T-bill ladder maturing near the due date can add yield without meaningful risk. Do not invest sinking funds in equities; the date is fixed and the market's is not." }, { "q": "Should I run several funds at once?", "a": "Yes, and most people do — sub-accounts or labelled buckets for insurance, car, home, travel. Total them and compare against your monthly surplus; if the sum exceeds what you have, extend the timelines or reduce the targets rather than underfunding everything equally." }, { "q": "Why include inflation on the item?", "a": "Because the target you priced today is not what you will pay in two years, especially for construction, insurance premiums, and vehicles. Growing the target keeps the fund from landing short at exactly the moment you need it whole." } ], "related": [ "https://www.revenuelab.fyi/toolbox/emergency-fund-target", "https://www.revenuelab.fyi/toolbox/savings-goal-date", "https://www.revenuelab.fyi/toolbox/buy-vs-lease-car" ], "license": "CC-BY-4.0", "citation": "RevenueLab — Sinking Fund Monthly Contribution Calculator (https://www.revenuelab.fyi/toolbox/sinking-fund-monthly)" }