24. Trade and other receivables
(a) Analysis by type and maturity
| 2022 US$m | 2021 US$m | |
| Trade and unbilled receivables | 1,083 | 923 |
| Credit note provision | (20) | (19) |
| Trade receivables – after credit note provision | 1,063 | 904 |
| Contract assets | 130 | 151 |
| Trade receivables and contract assets | 1,193 | 1,055 |
| Loss allowance | (22) | (23) |
| Net impaired trade receivables and contract assets | 1,171 | 1,032 |
| VAT and equivalent taxes recoverable | 4 | 5 |
| Prepayments | 279 | 220 |
| Contract costs | 88 | 100 |
| 1,542 | 1,357 | |
| As reported in the Group balance sheet: | ||
| Current trade and other receivables | 1,409 | 1,197 |
| Non-current trade and other receivables | 133 | 160 |
| 1,542 | 1,357 |
There is no material difference between the fair value and the book value stated above. Non-current trade and other receivables comprise prepayments, contract assets, unbilled receivables and contract costs.
At 31 March 2020, the value of trade and unbilled receivables was US$853m and contract assets was US$167m.
(b) Loss allowance matrix
| 2022 | 2021 | ||||
| Loss allowance US$m | Gross carrying amount US$m | Loss allowance US$m | Gross carrying amount US$m | ||
| Not past-due | (7) | 937 | (3) | 840 | |
| Up to three months past-due | (1) | 198 | (2) | 157 | |
| Three to six months past-due | (1) | 27 | (2) | 26 | |
| Over six months past-due | (13) | 31 | (16) | 32 | |
| Trade receivables and contract assets | (22) | 1,193 | (23) | 1,055 | |
| Loss allowance (note 24(c)) | (22) | (23) | |||
| Net trade receivables and contract assets | 1,171 | 1,032 | |||
(c) Movements in the loss allowance
| 2022 US$m | 2021 US$m | |
| At 1 April | 23 | 25 |
| Increase/(decrease) in the loss allowance recognised in the Group income statement | 3 | (1) |
| Receivables written off in the year as uncollectable | (5) | (2) |
| Differences on exchange | 1 | 1 |
| At 31 March | 22 | 23 |
(d) Analysis by currency denomination
| Contract assets | Trade receivables | ||||
| 2022 US$m | 2021 US$m | 2022 US$m | 2021 US$m | ||
| US dollar | 47 | 50 | 571 | 499 | |
| Brazilian real | 2 | 3 | 187 | 117 | |
| Pound sterling | 11 | 9 | 157 | 142 | |
| Euro | 27 | 32 | 50 | 55 | |
| Colombian peso | 2 | — | 14 | 13 | |
| South African rand | 5 | 10 | 10 | 7 | |
| Other | 36 | 47 | 52 | 48 | |
| 130 | 151 | 1,041 | 881 | ||