People type this into search every day: sinking fund calculator.
The usual answer is “target divided by months.” That is the cash version. It still needs the money already sitting there, and any gift or bonus you can count on before the bill.
This page is a labeled example. It is not a forecast of a savings APY, and it is not personalized financial advice.
A known bill, then a monthly slice
The CFPB savings plan worksheet is the same subtraction. Their example is an emergency fund of $1,000 in 10 months. Monthly amount: 1000 ÷ 10 = $100. No interest in that table.
Their goal-setting tool repeats the last step for any goal that needs money: figure out how much to set aside each week or month.
The Your Money, Your Goals life-events worksheet names the bills that belong here. A wedding, a car repair, a holiday, a move. Estimate the cost. Decide what you will save. Then use a plan so the monthly amount is visible.
A sinking fund is that plan for a bill you can see coming. An emergency fund is the pile for a bill you cannot see. The emergency fund target calculator sizes that pile. Keep the two accounts apart or the roof money disappears when the transmission goes.
The sinking fund contribution calculator uses this formula:
(future cost − already reserved − expected contributions) ÷ months ÷ contributors
The target cost does not change. No investment return is included. Those are the tool’s assumptions.
Fig 1
Gap first, then the month
Cash already reserved and one-off gifts come out before you divide
Subtract what you have and what you expect. Divide by the months. Split by the people paying.
If the money will sit for years and earn a return, the savings goal timeline is the closer tool. The monthly savings post walks that loop.
Example 1: the published $2,400 bill
Here are the calculator defaults:
- future cost: $2,400
- already reserved: $400
- expected one-off contributions: $0
- months remaining: 10
- people contributing: 1
Gap: 2400 − 400 − 0 = $2,000.00
Monthly: 2000 ÷ 10 = $200.00
Already funded: 400 ÷ 2400 = 16.7%
Calculator result
Sinking fund contribution
- Future cost
- $2,400.00
- Already reserved
- $400.00
- Expected one-off contributions
- $0.00
- Months remaining
- 10 months
- People contributing
- 1 people
$200.00
to set aside each month
- Total needed each month
- $200.00
- Amount still needed
- $2,000.00
- Already or externally funded
- 16.7%
$200.00 is the deposit that hits $2,400 in month 10 if the cost does not move and nobody adds a side gift.
Fig 2 · 1/2
The $2,400 pile
Defaults: $400 already there, 10 months left
Already reserved
$400.00
Still to save
$2,000.00
You already hold $400.00, 16.7% of the bill.
The remaining $2,000.00 is $200.00 a month for 10 months.
Fig 3 · 1/2
Ten $200 deposits
Start at $400. End at $2,400. No return in this model.
Saved now
$400
Month 10
The target next
$2,400
Month 0 is the $400.00 already reserved.
Month 10 is $2,400.00 if each deposit is $200.00.
The savings goal timeline calculator on the same $400, $2,400, $200, and 0% return prints 10 months and a final balance of $2,400.00. Same cash path. The sinking-fund tool is the one that starts from a deadline and gives you the monthly number.
Example 2: a $1,800 insurance bill
Annual premium, no cash set aside yet, 12 months.
- target: $1,800
- saved: $0
- expected: $0
- months: 12
Gap: $1,800.00
Monthly: 1800 ÷ 12 = $150.00
Calculator result
Sinking fund contribution
- Future cost
- $1,800.00
- Already reserved
- $0.00
- Months remaining
- 12 months
$150.00
to set aside each month
- Total needed each month
- $150.00
- Amount still needed
- $1,800.00
- Already or externally funded
- 0%
Example 3: $4,800 of property tax
Same 12-month clock, larger bill.
- target: $4,800
- saved: $0
- months: 12
Monthly: 4800 ÷ 12 = $400.00
That $400.00 is a reserve, not the tax office’s installment plan. If the county already splits the year, type the remaining installment and the months until it is due.
Example 4: an $3,000 trip with $500 already saved
- target: $3,000
- saved: $500
- expected: $0
- months: 8
Gap: 3000 − 500 = $2,500.00
Monthly: 2500 ÷ 8 = $312.50
Funded share: 500 ÷ 3000 = 16.7%
Calculator result
Sinking fund contribution
- Future cost
- $3,000.00
- Already reserved
- $500.00
- Months remaining
- 8 months
$312.50
to set aside each month
- Total needed each month
- $312.50
- Amount still needed
- $2,500.00
- Already or externally funded
- 16.7%
Example 5: a wedding split between two people
The wedding savings post builds the day first. This tool only funds a number you already have.
- target: $18,000
- saved: $2,000
- expected one-off: $1,500
- months: 14
- contributors: 2
Gap: 18000 − 2000 − 1500 = $14,500.00
Total each month: 14500 ÷ 14 = $1,035.71
Per person: 1035.71 ÷ 2 = $517.86
Funded share: 3500 ÷ 18000 = 19.4%
Example 6: what if the deadline halves
Keep the default $2,400 target and the $400 already saved. Cut the months from 10 to 5.
Gap is still $2,000.00
Monthly: 2000 ÷ 5 = $400.00
The deposit doubles because the calendar halved. The bill did not grow.
Fig 4 · 1/2
Same $2,000 gap, two clocks
Defaults, then a 5-month rush
- Monthly deposit
| Category | Monthly deposit |
|---|---|
| 10 months | $200 |
| 5 months | $400 |
10 months needs $200.00 a month.
5 months needs $400.00. The gap stayed $2,000.00.
Fig 5 · 1/2
Two paths to $2,400
Both start at $400. No return.
Balance
- $200 / 10 mo
- $400 / 5 mo
| Point | $200 / 10 mo | $400 / 5 mo |
|---|---|---|
| 0 | $400 | $400 |
| 2 | $800 | $1.2k |
| 4 | $1.2k | $2.0k |
| 6 | $1.6k | $2.4k |
| 8 | $2.0k | $2.4k |
| 10 | $2.4k | $2.4k |
The 10-month line adds $200 each month and finishes at $2,400.
The 5-month line adds $400 and gets there in half the time.
Example 7: the common mistake, ignore the $400 already saved
Type the $2,400 target, leave saved at $0, keep 10 months.
Monthly: 2400 ÷ 10 = $240.00
The real deposit is $200.00. The extra $40.00 a month is you funding cash you already have. Over 10 months that is $400.00, the reserved pile counted twice.
Fig 6 · 1/2
Counting the $400 twice
Same $2,400 target and 10 months
Each month
With $400 saved
$200
Saved left at $0
$240
The correct deposit is $200.00 after the $400.00 reserved.
Ignore the reserved cash and the tool asks for $240.00.
Example 8: a bonus that covers the rest
Keep the $2,400 target and the $400 reserved. A $2,000 bonus lands before the due date.
- expected: $2,000
- months: 10
Gap: 2400 − 400 − 2000 = $0.00
Monthly: $0.00
Funded share: 100%
The tool will not invent a deposit once the gap is gone. If the bonus is not certain, leave expected at $0 and keep transferring $200.
Example 9: a $900 repair in 3 months
- target: $900
- saved: $0
- months: 3
Monthly: 900 ÷ 3 = $300.00
Short deadlines make a sinking fund look like a second rent. That is the point of starting earlier, not a reason to skip the account.
Example 10: the bill is already funded
- target: $2,400
- saved: $2,400
- months: 10
Monthly: $0.00
Funded share: 100%
Stop the transfer, or point the same $200 at the next known bill.
Example 11: $12,000 for a roof in 24 months
- target: $12,000
- saved: $0
- months: 24
Monthly: 12000 ÷ 24 = $500.00
The roofing quantity post turns a footprint into bundles. This $12,000 is a cash target you typed, not a contractor quote. The home maintenance reserve is the broader monthly allowance. A sinking fund is the named project inside that allowance.
The eleven deposits next to each other
| Example | Target | Already in | Expected | Months | People | Monthly |
|---|---|---|---|---|---|---|
| 1. Default bill | $2,400 | $400 | $0 | 10 | 1 | $200.00 |
| 2. Insurance | $1,800 | $0 | $0 | 12 | 1 | $150.00 |
| 3. Property tax | $4,800 | $0 | $0 | 12 | 1 | $400.00 |
| 4. Trip | $3,000 | $500 | $0 | 8 | 1 | $312.50 |
| 5. Wedding, two people | $18,000 | $2,000 | $1,500 | 14 | 2 | $517.86 each |
| 6. Five-month rush | $2,400 | $400 | $0 | 5 | 1 | $400.00 |
| 7. Forgot the $400 | $2,400 | $0 | $0 | 10 | 1 | $240.00 |
| 8. Bonus covers it | $2,400 | $400 | $2,000 | 10 | 1 | $0.00 |
| 9. Repair | $900 | $0 | $0 | 3 | 1 | $300.00 |
| 10. Already funded | $2,400 | $2,400 | $0 | 10 | 1 | $0.00 |
| 11. Roof cash | $12,000 | $0 | $0 | 24 | 1 | $500.00 |
Open the sinking fund calculator with the remaining bill, the cash already parked, and the months on the calendar. If the date is years away and you want a return in the model, switch to the savings goal timeline.