Hour bank calculator: balance and overrun

An hour bank is a number of hours a client buys in advance for a period. Each month the hours used come off it, and what is left carries into the next month under the agreed rule. Enter your numbers: the calculator shows the balance for every month and flags an overrun early. It runs in your browser and saves nothing.

Hours bought each month

If the bank was bought once, enter 0 and fill in the opening balance.

Opening balance (hours) Hours used per month, on average

Number of months

Hourly rate

Optional. Without a rate, only hours are counted.

Unused hours

Overrun Carries into the next month as debt Paid every month, the balance never goes below zero

Result

240

Hours bought

276

Hours used

-26

Balance at the end

The bank runs out in month 2. Tell the client now, not on the invoice. Every month uses 6 h more than is bought.

Balance month by month, in hours
Month	Opening	Bought	Used	Closing
1	10	40	46	4
2	4	40	46	-2
3	-2	40	46	-8
4	-8	40	46	-14
5	-14	40	46	-20
6	-20	40	46	-26
Total		240	276	-26

Overrun at the end of the period: 26 h at 275 per hour, 7,150 before tax.

The calculation runs in your browser and is not saved anywhere.

How the calculator counts

Each month is one row of the table: the opening balance, plus the hours bought, minus the hours used, gives the closing balance. The closing balance is the next month's opening balance, exactly as in the hour bank tracker template.

Hours bought each month are added at the start of every month. If the bank was bought once, enter 0 here and put the whole bank in the opening balance;
Opening balance is what is in the bank before the first month. It counts as bought in month 1;
Hours used per month is an average. For a real check, take the number from the monthly report, not from an estimate;
Hourly rate is optional. Without it the calculator counts hours only.

Hours are always used oldest first: the hours that would expire soonest go first.

Carry-over rules

What happens to unused hours depends on the agreement, so the calculator offers three rules:

Carry over for up to 3 months. Hours not used in the month they were bought can still be used in the next three months. At the end of the third month, whatever is left of them expires;
Do not carry over. Whatever is not used by the end of the month expires;
Accumulate without limit. Nothing expires, and the balance grows until it is used.

Expired hours appear in a separate column, and their total is shown under the result. If your agreement says something else, for example two months or six, pick the closest rule and keep the difference in mind.

Overrun: debt or paid every month

When a month uses more hours than the bank holds, there are two common ways to settle it, and the calculator shows both:

As debt. The balance goes below zero and the minus carries into the next month, as in the Excel template. New hours pay off the debt first. The cost of the overrun at the end of the period is shown under the table;
Paid every month. The balance never goes below zero. The excess of each month is shown separately, in the "to pay" column, and the next month starts again from the hours bought.

With the same numbers the total overrun is usually the same. What changes is when it is paid: at the end of the period, or every month.

What to do with the result

The bank runs out in a given month: tell the client now, not on the invoice, and agree in advance whether to buy another bank or bill the extra hours at the rate;
The balance stays negative month after month: the bank is smaller than the real need. That is a conversation about the size of the bank, not about one month's overrun;
Hours expire every month: the bank is bigger than the need, or the carry-over rule is too short. It is better to raise this before the client does.

The calculator assumes the same usage every month. Real months differ, so for tracking month by month use the tracker template with the actual hours.

Frequently asked questions

How does the hour bank calculator work?

Each month it adds the hours bought to the balance and subtracts the hours used. Hours are used oldest first, and unused hours carry over or expire under the rule you pick. The result is a table with the opening and closing balance of every month, the month the bank runs out, and the overrun in hours and, if you enter a rate, in money.

Is my data saved anywhere?

No. The calculation runs in your browser, and the numbers you enter are not sent to the server or stored. When you close the page, they are gone.

What is the difference between an overrun as debt and paying it every month?

As debt, a negative balance carries into the next month and new hours pay it off first, as in the Excel template. Paid every month, the balance never goes below zero: the excess of each month is paid separately, and the next month starts from the hours bought. With the same numbers the total overrun is usually the same; what changes is when it is paid.

Why does the calculator show expired hours?

Because under some agreements unused hours do not carry over forever. If the rule is "up to 3 months" or "does not carry over", hours not used in time expire, and the client has paid for them without getting work. Seeing this in advance is a reason to change the size of the bank or the rule.