Purchase budget calculator

What it works out

The purchase budget calculator turns records from the business into a figure for this decision: how much material to buy for next month's plan. Use it when the responsible stores manager and purchase manager needs a consistent answer for this specific task. The answer uses only the values entered. Record the measurement period beside it.

What you need

Use the same item, period and measurement unit for related inputs. If a figure comes from an estimate rather than an actual record, mark it as estimated. Keep your original figures beside the result.

The formula

In plain words, calculate purchase budget using the measured inputs below. The expressions are shown without hidden rounding so they can be checked by hand.

• quantity to buy: quantity_to_buy = planned_output*material_per_unit*(1+wastage_percent/100)-opening_stock+target_closing_stock.
• purchase budget: purchase_budget = quantity_to_buy*material_rate.

Formula basis from the supplied taxonomy: quantity to buy = planned output x material per unit x (1 + wastage %) - opening stock + target closing stock; budget = quantity x rate. The calculation assumes the named inputs describe the same job and accounting period. Keep quantities, rates and measured units consistent.

A worked example

Illustrative example: a garment unit uses the figures in the table above. These are example inputs, not industry averages. For this example, the main figures are planned output: 3,600, material per unit: 1.70 kg/unit, wastage percent: 6 %, opening stock: 1,250.

1. Quantity to buy: planned_output*material_per_unit*(1+wastage_percent/100)-opening_stock+target_closing_stock. With the example figures, 3600.0 * 1.7 * (1 + 6.0 / 100) - 1250.0 + 1800.0 gives 7,037.20.
2. Purchase budget: quantity_to_buy*material_rate. With the example figures, 7037.2 * 58.0 gives ₹4,08,157.60.

How to act: Use the result to compare it with the next purchase date. Write down the input date and the assumption that could move most.

How to read the result

Example bands, change them for your business:

• Comfortable: Your result meets the target for this item or reporting period. Keep the calculation with its source records and compare it with the next purchase date.
• Watch: The result is close to your action limit, or it changed since the previous calculation. Recheck planned output and material per unit using the original records.
• Act: The result breaks a limit already agreed by the manager or owner. Record the difference, name a responsible person, and agree a correction date. For an operational starting point, read [Material shortages](/problems/material-shortages) and [Purchase requirement to material received](/processes/purchase-requirement-to-material-received). Do not use these example bands as published industry benchmarks.

Copy it into a spreadsheet

Create a sheet with column A for the label and column B for the number or formula. The expressions work in Excel or Google Sheets. Keep input cells editable and result cells protected from typing.

For any formula containing a divisor, enter a value above zero. For any monetary output, format the cell in Indian rupees. Do not replace the cells with rounded figures until the final display.

What this calculator leaves out

• Demand jumps, seasonality, minimum supplier order sizes and rejected receipts can change the decision.
• A single average can hide unusual lots, customers or weeks. Review the underlying entries before making a large decision.
• The formula does not check whether the records are complete. Check the stores register and the open PO list before buying. A number from last quarter may no longer represent the next delivery.

Common mistakes

1. Mixing periods. Using planned output from one month with material per unit from another produces a number that looks precise but is hard to act on.
2. Trusting old figures. Recheck the relevant source record before reusing last month's saved inputs. If the calculated number conflicts with a physical stock count, reconcile the shelf and the book before placing an order.
3. Treating an estimate as approval. Record which assumptions were entered by hand. Get the relevant owner, accountant or technician to check unusual values.

A number like this helps only if someone works it out again when things change.

Questions people ask

Where do I find the numbers for purchase budget calculator?

Read planned output from the job card, shift report, machine log or maintenance register. Check the stock ledger, stock count, approved BOM or last receipt for material per unit. Keep all inputs from the same period.

Can I use this number to approve a purchase or payment?

Use it as a first check. Use the result to compare it with the next purchase date. Write down the input date and the assumption that could move most. If the result affects tax, legal duties, workplace safety or a major investment, obtain the appropriate review.

When should I calculate it again?

Recalculate when a meaningful input changes, and at the next regular review of the relevant register. Save the date and the input values so changes can be explained.