Here's the short answer. Take the total cost, subtract what you've already saved, and divide by the number of months until you want to buy. If the item costs $1,200 and you want it in six months, you need to save $200 a month.
A few adjustments make that number more realistic: a buffer for surprise costs, a check that it fits your budget, and a plan for what to do if it doesn't. This guide covers each one so you can pick a monthly amount you can actually keep up.
The basic formula
Monthly savings = (Purchase cost + buffer − money already saved) ÷ months until purchase
That's the core of a sinking fund, which means setting money aside bit by bit for a specific planned expense. Capital One describes a sinking fund as a way to pay for planned costs like cars, vacations or home projects without relying on credit.
Step 1: Pin down the real cost
Start with the full price you expect to pay, not just the sticker price. Depending on the purchase, that can include:
- Sales tax (rates differ by country, state and city)
- Delivery, installation or setup fees
- Accessories you'll need right away, like a case for a laptop or a mattress protector for a new bed
- Registration, insurance or other fees for a vehicle
Step 2: Add a buffer
Prices change and small extras pile up. Associated Bank suggests adding about 10–15% to your goal to cover inflation and unexpected costs. If your estimate is already solid, use the low end. If you're still guessing, use the high end.
Step 3: Subtract what you already have
Count only money you've truly set aside for this goal. Your emergency fund doesn't count. That money is for job loss, medical bills and other surprises, and mixing the two can leave you exposed.
Step 4: Divide by your timeline
Count the months you have left, and be honest about it. A shorter timeline means a bigger monthly amount, and a longer one means a smaller amount.
Hypothetical examples
These scenarios are illustrative only, using a 10% buffer:
| Goal | Cost + 10% buffer | Already saved | Months | Monthly amount |
|---|---|---|---|---|
| Laptop | $1,200 + $120 = $1,320 | $0 | 6 | $220 |
| Vacation | $3,000 + $300 = $3,300 | $500 | 10 | $280 |
| Car down payment | $5,000 + $500 = $5,500 | $1,400 | 18 | $228 (rounded up) |
Round up rather than down. A few extra dollars a month is easier to manage than coming up short at the end.
Convert it to your pay schedule
If you're paid every two weeks, a monthly target can feel abstract. To turn it into a per-paycheck amount:
Per paycheck (biweekly) = Monthly amount × 12 ÷ 26
For example, $280 a month works out to about $129 per biweekly paycheck. Moving that amount on payday, before you have a chance to spend it, is one of the simplest ways to stay on track. Automating regular transfers is a common savings tip because the money gets saved without you having to decide each time.
Check whether the number fits your budget
A monthly target only helps if your budget can hold it. NerdWallet points out, as reported by CPA Practice Advisor, that sinking fund contributions work as an affordability test. If you can't fit the monthly payments into your budget now, you probably can't afford the purchase later without borrowing.
To find room:
- Look at what you actually spent last month, then set smart category caps using last month's spending to free up a realistic amount.
- Send any extra toward the goal. If you're not sure how, here's what to do with money left at month-end.
- Before you commit, ask whether the purchase earns its cost. The price-per-use rule can help you decide if it's worth saving for at all.
If the monthly amount is too high
Finding out your target doesn't fit isn't a failure. It's useful information. You have four levers to work with:
- Extend the timeline. In the vacation example above, stretching 10 months to 14 drops the monthly amount from $280 to $200.
- Lower the cost. Look at a refurbished model, a used version, an off-season date or a simpler option.
- Start with a bigger lump sum. A tax refund, a bonus or money from selling things you don't use can shrink the remaining gap.
- Earn a bit more for a while. Extra shifts or a short side project can speed things up. Keep it temporary so you don't burn out.
You can also combine levers. A slightly longer timeline plus a slightly cheaper option often lands on a number that feels comfortable.
Saving for several goals at once
If you're saving for more than one thing, work out the monthly amount for each goal separately, then add them together. The total is what your budget actually has to cover.
When the total is too much, rank your goals. Fully fund the most important or most time-sensitive one first and give the others smaller amounts. A purchase queue can prevent budget pileups by lining up big buys one at a time instead of letting them all land in the same month.
Where to keep the money
Keep your big-purchase savings somewhere separate from your everyday spending money, so it's harder to dip into by accident. A few points to weigh:
- Interest is a bonus, not the plan. In the US, the FDIC reported a national average savings rate of 0.38% APY in mid-2026 (FDIC National Rates and Rate Caps, July 2026). At that rate, a $3,000 balance earns roughly $11 in a year. High-yield accounts often pay more, but over a short timeline the interest won't change your monthly target much.
- Check deposit protection. In the US, the FDIC insures deposits at insured banks up to $250,000 per depositor, per bank, per ownership category. Other countries have their own deposit guarantee schemes and limits.
- Avoid riskier investments for short-term goals. If you need the money within a few years, a drop in the market could leave you short right when it's time to buy.
Why saving first usually beats financing
Buying on credit adds interest to the price. In the US, the average interest rate on credit card accounts that were charged interest was 22.15% in May 2026, according to the Federal Reserve's G.19 consumer credit release. Saving ahead means the price you plan for is the price you pay.
Paying cash also gives you some breathing room. If you change your mind halfway through, the money is still yours. Once the purchase is made, watch out for follow-up spending. Here's how to stop one purchase from triggering a spending chain.
Tracking your progress
Seeing the balance grow keeps you motivated, so pick a simple way to track it. If you use Monee, its unlimited accounts can be set up "for different people, goals, or projects." That lets you give a big purchase its own account. Monee also lets you carry your remaining balance over to the next month and set your financial month to start on any day you like, such as your payday. It doesn't list a dedicated savings-goal feature, so you'd still do the monthly math yourself using the formula above.
Whatever tool you use, check in once a month:
- Are you on pace?
- Has the price or your timeline changed?
- Do you need to adjust your monthly amount?
Quick recap
- Formula: (Cost + buffer − saved) ÷ months left
- Buffer: Add about 10–15% for surprises
- Fit test: If the monthly amount doesn't fit your budget, change the timeline, the cost or your income
- Several goals: Work out each one, then add them up and rank them
- Storage: Keep the money separate, safe and easy to reach
A big purchase is mostly a math problem with a timeline attached. Once you know your monthly number and set it aside on payday, every transfer gets you closer, and you can do this one month at a time.
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