---
title: "How to model a seasonal or one-off cost in sherloc"
url: "https://help.sherloc.elementaryb.com/en/article/how-to-model-a-seasonal-or-one-off-cost-in-sherloc"
language: "en"
last_updated: "2026-10-05T21:40:38.908Z"
---

# How to model a seasonal or one-off cost in sherloc

For a cost that only applies for a short window (a busy-season top-up, a single bonus, a one-off project cost), you only want it showing up in the months it actually happens.

## 1\. Confirm the cost and the months it applies to

Work out how much extra cost you want in each month, and exactly which months it falls in: this might be one month, or a short run of months.

Example: taking on extra temporary staff over the festive period, at an extra £2,000 in each of November and December.

## 2\. Add it as an assumption on the relevant line

Select **Create assumption**. In the **Create Assumption** drawer, give the assumption a name (this is required), then choose the sheet that holds your costs from the **Select the sheet impacted by the assumption** dropdown: for example **Profit And Loss**. Tick the cost line it applies to in the list of row items, then select **Continue to date range**.

Under **When should the assumption happen**, choose **Date range** and set a **From** and **To** month, covering just the months the cost applies to, not the whole year. If the months aren't next to each other, choose **Specific months** instead. Then select **Continue to criteria**.

Under **What the assumption is modelling**, choose **Increase / decrease**, keep **£ Fixed amount** selected, and enter the extra cost for one month in **How much?** (or choose **Replace the figure** if you'd rather set the month to a figure than add to it). Finish with **Add assumption**.

The amount you enter is applied to each month you've selected, so it isn't shared out between them.

Example: enter 2,000 for November and December. £2,000 is added to each of the two months, so £4,000 in total.

## 3\. Check the numbers

Look at your Profit And Loss sheet to confirm the cost only appears in the months you selected, and that your other months are unaffected. Under **Accounts & Assumption Details** you can see the line's **Base** figure, your assumption and the **Result** for each month.